Mocks & Spies in Minitest

For one of our smaller ruby projects we didn't want to bring in all of rspec, so we decided to go with minitest as our unit test runner and assertion library. Doing mocks and spies in minitest proved a little bit challenging to get the hang of initially but it's actually quite easy. This article will explain how to do it.
Written on August 5, 2020 by podrezo
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Ruby code with gems on AWS Lambda

If you want to use ruby with AWS's lambdas and that ruby code relies on gems then you'll have to jump through a small hoop to get it running. This article explains how. [Continued...]
Written on August 4, 2020 by podrezo
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Using AWS Lambdas and API Gateway together: Function Policies

If you want to use a custom route for your lambda, and not just the generated route given by adding your lambda to your gateway automatically, you'll need to specifically enable a "function policy" to do so. The current function policy can be viewed by going to the lambda in the AWS console, going to "permissions" and scrolling down to the "function policy" section. This provides a read only, JSON-formatted view of the function policy for the lambda you're looking at. This view is read-only: It is not possible to manipulate the function policy from the AWS console and modifying it will require the use of either the AWS API or the [AWS CLI]( For the purposes of this post, we'll use the CLI. [Continued...]
Written on December 20, 2019 by podrezo
Read More with a block

I was recently following a great blog article on memoization in Ruby by Justin Weiss and it made perfect sense until I got to the last part which was most relevant for my purposes - "And what about parameters?". Here, the article uses a pattern of memoization that involves a `` that is supplied a block. [Continued...]
Written on November 27, 2019 by podrezo
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Apollo flattens your GraphQL data!

Suppose we’re retrieving items in an eCommerce cart:

query {
  cartItems() {
    item {
      product {

Data is returned as expected.

  cart_items: {
    0: {
      product: {
        id: "nulogy-shirt",
        size: "medium",
    1: {
      product: {
        id: "nulogy-shirt",
        size: "large",

In our cart, we have two nulogy-shirt items. One is medium, one is large, so they’re not quite the same product. When this data hits Apollo, however…

  cartItems: {
    0: {
      product: {
        id: "nulogy-shirt",
        size: "medium",
    1: {
      product: {
        id: "nulogy-shirt",
        size: "medium",

All the data is stored in Apollo’s cache as a flattened array. Regardless of how they’ve been nested inside other objects, no two objects of the same type can share an ID. Otherwise, the first object overwrites all others.

Apollo makes this comparison based on the id or _id field (or a user override). If not found, the object’s keys become dependent on the nesting (ROOT_QUERY.cartItems.0.product and ROOT_QUERY.cartItems.1.product)

If you experience this, a good solution is to rename the ID field for the query’s response.


Written on September 6, 2019 by devanhurst
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Slow Terminal Startup Tip: Lazy Load NVM

For a long time, my ZSH shell windows/tabs have had very slow startup times, sometimes taking 5-10 seconds before .zshrc fully loads and the input cursor appears. This slows down my daily development cycles.

It turns out that loading NVM was the main culprit. Using this Medium post and this gist as motivation, I have added this snippet to my .zshrc file in order to lazy load nvm, npm, node, and npx (copied from the gist, credit goes to that author). I have immediately observed major speed improvements in my shell speed load times.

lazynvm() {
  unset -f nvm node npm npx
  export NVM_DIR=~/.nvm
  [ -s "$NVM_DIR/" ] && . "$NVM_DIR/" # This loads nvm
  if [ -f "$NVM_DIR/bash_completion" ]; then
    [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion" # This loads nvm bash_completion

nvm() {
  nvm $@
node() {
  node $@
npm() {
  npm $@

npx() {
  npx $@
Written on August 8, 2019 by evanbrodie
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Improve macOS Performance with Spotlight Privacy

File contents indexing on macOS is performed by Spotlight. You can reduce Spotlight’s activity by excluding directories such as:

  • ~/src
  • ~/Library/Caches/
  • ~/Library/Containers/com.docker.docker/
  • ~/Library/Containers/com.docker.helper/

Go to System Preferences > Spotlight > Privacy and get yourself a faster machine.

Written on July 18, 2019 by alistairmckinnell
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Finding a Rake Task Definition

Suppose you use a certain Rake task. Is there an easy way to find out where that task is defined?

There is. Use the ` –where` option.

Example: rake --where packman:update

Written on June 4, 2019 by alistairmckinnell
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Ignore some paths from git diff


I want to do a git diff, but I need some paths to be ignored.

e.g. git diff --name-only



What I want:



Git pathspecs!

“After a path matches any non-exclude pathspec, it will be run through all exclude pathspecs (magic signature: ! or its synonym ^). If it matches, the path is ignored.”

git diff --name-only -- '!**/ignore_me/*'

Written on April 8, 2019 by clemenspark
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Disable special characters in OS X (no 3rd party)

RubyMine comes with handful of mnemonics which are supposed to boost your productivity. However ones that are combined with alt keys can sometimes cause unexpected behaviours since some of them are bound to special characters (e.g. ™, Ó, µ …).

You can disable special characters by choosing “Unicode Hex Input” as an input source (System Preferences > Keyboard > Input Sources > Others).

Now typing Alt + key won’t interfere with any keyboard shortcuts. Happy RubyMining!

Written on February 25, 2019 by jiyou
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Lazy-load NVM to speed up zsh initialization

UPDATE Once appending --no-use, ensure to source $NVM_DIR/ when actually needed. For example, yarn install will complain ` node: No such file or directory`

I was curious as to why the zsh initialization was so slow. After some benchmarking .zshrc, I learned that oh-my-zsh and NVM were the main source of slow-down. For oh-my-zsh, I’m trying to see if I can avoid loading plugins that I rarely use to cut some time. However for nvm, simply passing `–no-use the following will make a big difference.

[ -s "$NVM_DIR/" ] && . "$NVM_DIR/" --no-use

Benchmarking with bash’s buil-in time command…

Before --no-use:

❯ for i in $(seq 1 5); do /usr/bin/time zsh -i -c exit; done
        1.43 real         0.65 user         0.62 sys
        2.42 real         0.66 user         0.61 sys
        1.42 real         0.65 user         0.61 sys
        1.42 real         0.65 user         0.61 sys
        2.43 real         0.66 user         0.62 sys

After --no-use:

❯ for i in $(seq 1 5); do /usr/bin/time zsh -i -c exit; done
        0.48 real         0.26 user         0.17 sys
        0.46 real         0.25 user         0.16 sys
        0.46 real         0.25 user         0.16 sys
        0.46 real         0.26 user         0.16 sys
        0.49 real         0.27 user         0.17 sys


Written on February 19, 2019 by jiyou
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Rebase your branch from one branch to another

Use: git rebase --onto new-base-branch current-base-branch

For example, let’s say we have a feature branch based on master, and we decided it’s better to rebase it off production. This is our current git history:

commit 6 [my-feature-branch]
commit 5
commit 4 [master]
commit 3
commit 2 [production]
commit 1

We just need to run:

git checkout my-feature-branch
git rebase --onto production master

And we will end up with the following history:

commit 6 [my-feature-branch]
commit 5
commit 2 [production]
commit 1


Written on August 16, 2018 by arturopie
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Use Chrome to make "desktop apps"

You can use Chrome to make slick desktop apps for your frequently used tabs, and even make aliases:

alias twitter="open -na 'Google Chrome' --args '--app='"

# replace #{UID} with the index of the google account you want to use
# if you are signed in to multiple accounts on your computer, otherwise 0 should be fine.
alias cal="open -na 'Google Chrome' --args '--app={UID}/r'"

# for fun
alias pm="open -na 'Google Chrome' --args '--app='"

Original tweet:, credits to Elijah Manor!

Written on August 8, 2018 by jasonkurian
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Before Callback Changes in Rails 5

In Rails 4 and below, callbacks like before_validation always had a gotcha that you had to watch out for:

before_validation :ensure_field_is_false_when_condition

def ensure_field_is_false_when_condition
  self.field = false if condition?

When condition? is true, the assignment happens. However, assignment returns the value that was assigned, so the before_validation receives the returned value false. As the docs mention:

If the returning value of a before_validation callback can be evaluated to false, the process will be aborted and Base#save will return false.

This is usually handled by an explicit return (i.e. nil does not stop the callback chain):

def ensure_field_is_false_when_condition
  self.field = false if condition?
  # extraneous return that is not Ruby-ish

Rails 5 Update

There is a great change to the before_validation callback behaviour in Rails 5:

If the before_validation callback throws :abort, the process will be aborted and ActiveRecord::Base#save will return false.

This makes halting the callback chain much more transparent and intention revealing:

before_validation :safely_assign_false, :always_halt_validation

def safely_assign_false
  self.field = false

def always_halt_validation
Written on August 8, 2018 by jasonschweier
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Accessing Redux Store Without Redux DevTools

Thank you Dan Ambrogio for discovering this tip. Also, check out this blog post for more on the topic of Redux DevTools on production environments.

Let’s say that you want to access the Redux Store on a production environment of your React/Redux application. Normally, you would do this through the Redux DevTools. However, your app has these DevTools disabled on production. What do you do then?

As long as your browser has the React DevTools installed, there’s this awesome workaround (assuming you are using Chrome, could easily be ported to other browsers):

  • Navigate to the web page in question
  • Open up the Chrome DevTools
  • Click on the React tab
  • Click on the top-level <Provider> element/component
  • Press <ESC> to bring up a console in a split panel
  • Execute the following code: $ VOILA!
Written on August 2, 2018 by evanbrodie
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Hash keys must be symbols for keyword arguments

Recently our team worked on a ticket which required us to remove the tooltips for Edit, Delete button.

As an initial approach, we changed the signature by parameterizing the tooltip, and inserted into #link_to helper. To preserve the options parameter, we converted it into a keyword argument (**options).

def link_to_delete_remote(object, path, tooltip: _("Delete"), **options)
   link_to(options[:title], path, options.merge('data-bad-after': js, id: link_id, title: tooltip, remote: true))
 <%= link_to_delete_object(job, tooltip: nil) %>

However, bunch of specs started failing with the following message.

# ArgumentError: wrong number of arguments (given 3, expected 2)

Turns out, there were few callers of the method who were passing in an object that contains String keys, and they weren’t being used as keyword arguments…

<%= link_to_delete_object(
      "some-string-key" => _("some_string_value"),
      "another-string-key" => true
    ) %>

In the end, we reverted the signature, injected tooltip: nil to options object, and just inlined options.fetch(:tooltip, _(“Delete”))

  def link_to_delete_remote(object, path, options = {})
    link_to(options[:title], path, options.merge('data-bad-after': js, id: link_id, title: options.fetch(:tooltip, _("Delete")), remote: true))

Written on July 13, 2018 by jiyou
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Dig-ging into Data

Ruby 2.3 added a couple of dig methods to aid in accessing nested data.

Here’s some Hash and Array examples:

hash = {
  animals: {
    furry: ["dog", "cat"],
    spikey: ["porcupine", "echidna"]

hash.dig(:animals, :furry)
# => ["dog", "cat"]

# safely returns `nil` for missing keys
hash.dig(:plants, :yellow)
# => nil

array = [1, [[2, 3], 4, 5], 6]

array.dig(1, 0, 1)
# => 3

# dig on arrays take indexes, and repeatly call dig on the result
# thus, you have to be careful if the return type is not an array!
# => 6

array.dig(2, 3)
# => TypeError: Fixnum does not have #dig method

# and duck typing means they can be combined!
hash.dig(:animals, :spikey, 1)
# => "echidna"
Written on June 27, 2018 by jasonschweier
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Finding Where Rake Tasks Are Defined in Rails

Rake has an option to print where a task was loaded from.

$ rake -W gettext:find
rake gettext:find   $HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:64:in `block in <top (required)>'

We can also get this data with code. This allows us to explore the tasks (e.g. filtering). In a Rails console:

# load up all the tasks Rails knows about
> Rails.application.load_tasks

# if you know the task you are looking for:
> Rake::Task["gettext:find"]
 => [["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb", 64]]
 # if you want to explore known tasks
 > gettext_tasks = { |e| "gettext:" }
 => [<Rake::Task gettext:add_language => [environment]>, <Rake::Task gettext:base_without_table_attributes => [environment]>, <Rake::Task gettext:find => [setup]>, <Rake::Task gettext:pack => [setup]>, <Rake::Task gettext:setup => [environment]>, <Rake::Task gettext:store_model_attributes => [environment]>]
 > pp Hash[ { |t| [, t.locations] }]
  ["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:99:in `block in <top (required)>'"],
  ["$HOME/src/packmanager/master/lib/tasks/gettext.rake:27:in `block in <top (required)>'"],
  ["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:64:in `block in <top (required)>'"],
  ["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:59:in `block in <top (required)>'"],
  ["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:43:in `block in <top (required)>'"],
  ["$HOME/.rvm/gems/ruby-2.3.3/gems/gettext_i18n_rails-1.8.0/lib/gettext_i18n_rails/tasks.rb:82:in `block in <top (required)>'"]}
Written on June 26, 2018 by jasonschweier
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React Synthetic Events

React is awesome! Because it helps with making consistent event handler functions [among many other things].

Every event handler will be passed instances of SyntheticEvent which has consistent properties [as opposed to the native events’ variations in properties].

Written on June 20, 2018 by jasonkurian
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How to trigger a redeploy on ECS from web console

Sometimes, there is a neeed to trigger a redeploy on an ECS service without making any task changes (for example: rerun initialization scripts to pull secret updates). To trigger such a redeploy on an ECS service from the web console:

  1. Open the ECS service module on the AWS web console
  2. Click on the Cluster, then the Service you wish to trigger the redeploy on
  3. Press the Update button on the top-left
  4. Select the “Force new deployment” checkbox. Make no other changes. Press on the Next Step button.
  5. Click “Next Step” and “Confirm” on all subsequent screens without making any other changes.

You can observe that the process is a success by watching the Events tab for new tasks startin and old tasks stopping, and the Tasks tab to witness the new tasks go live.

Written on June 15, 2018 by evanbrodie
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What does the zeus's read unix EOF error mean?


I’m running zeus, and it dies with the following error:

slavenode.go:226: [boot] read unix ->: EOF

What on Earth could be causing that? How do I fix it?


UPDATE (2018-06-13): I realized that this is one possible fix to this issue. Still useful info, so I’ll leave it here.

Run bundle install


Written on June 12, 2018 by clemenspark
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ORDER BY NULL Sorting Options

The ORDER BY clause has options for placement of NULL columns. From the Postgres docs, the ORDER BY grammar is:

[ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]

It shows we can put the NULL columns first or last.


Imagine we have a datetime range, implemented as (start_at, end_at) tuples.

CREATE TABLE dates (id INT, start_at TIMESTAMP, end_at TIMESTAMP);

(1, TIMESTAMP '2018-01-01 9:45', TIMESTAMP '2018-01-01 10:00'),
(2, TIMESTAMP '2018-01-01 10:00', null),
(3, TIMESTAMP '2018-01-01 10:15', null);

We want to order by end_at, then start_at. However, we want the NULL end_at tuples to appear before any with a value.

By default, NULL values will appear after non-NULL. With the NULLS FIRST option, we can change that:

SELECT * FROM dates ORDER BY end_at NULLS FIRST, start_at, id;

│ id   │ start_at            │ end_at              │
│ 2    │ 2018-01-01 10:00:00 │ <null>              │
│ 3    │ 2018-01-01 10:15:00 │ <null>              │
│ 1    │ 2018-01-01 09:45:00 │ 2018-01-01 10:00:00 │

You can also specify NULLS when creating indexes too.

Written on March 12, 2018 by jasonschweier
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Move cursor word by word on iTerm


Cursor navigation can be slow on iTerm


Enable word by word cursor movement

Preferences > Profiles > Keys > Select + to add new key mapping

To move left:

Keyboard Shortcut: ⌥ ←
Action: Send Escape Sequence
Esc+ b

To move right

Keyboard Shortcut: ⌥ →
Action: Send Escape Sequence
Esc+ f


Written on February 8, 2018 by robertdooley
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Def keyword can also be used as a begin statement

In Ruby, the begin keyword for exception handling (ie, begin...rescue...ensure, traditionally try...catch...finally in other languages) is optional. You can have a method that only declares a rescue or an ensure statement without begin. That’s because the def statement in the method can serve the same purpose as begin. This means that this method:

def edit
    @user = find(params[:id])
  rescue ActiveRecord::RecordNotFound
    redirect_to :back

Can legally be shortened to:

def edit
  @user = find(params[:id])
rescue ActiveRecord::RecordNotFound
  redirect_to :back
Written on February 1, 2018 by evanbrodie
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Safe Navigation Operator

If you have worked in a Rails project, you have probably came across the try and try! methods. try saves us from checking conditions before drilling-down through a message chain. try! is more restrictive; it raises when the receiver does not respond to the method:

require "active_support"
require "active_support/core_ext/object/try"

User =

users = ["Jason")]

# "Jason"

# nil

# NoMethodError: undefined method `unknown_method' for #<struct User name="Jason">

Note these methods are provided by ActiveSupport. As of Ruby 2.3, this behaviour is now available in the language, called the safe navigation operator &.:

users = [ "Jason")]
# "Jason"

users = []
# nil


When an object does not respond to a method, &. behaves like try!; it raises an error. However, nil seems to break this pattern:

# behaviour like try!
# NoMethodError: undefined method `unknown_method' for #<struct User name="Jason">

# given that
# true

# this is confusing
# nil

The last example has a simple explanation: &. checks the receiver. Since the receiver is nil, &. immediately returns nil. It does not matter that nil responds to the message.

Written on January 29, 2018 by jasonschweier
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Block Kwargs

Ruby 2.0 introduced keyword arguments. Ruby 2.1 further added required keyword arguments. It is common to see methods using kwargs:

def some_method(keyword_arg: "Hello", required_arg:)
  puts "#{keyword_arg} #{required_arg}"

some_method(required_arg: "world")
# Hello world

However, these changes also apply to block arguments:

define_method :prints_block_arguments do |default_arg: "hello", required_arg:, **others|
  puts "default_arg: #{default_arg}"
  puts "required_arg: #{required_arg}"
  others.each_pair do |key, value|
    puts "other arg: #{key} => #{value}"

prints_block_arguments(required_arg: "world")
# default_arg: hello
# required_arg: world

prints_block_arguments(default_arg: "ciao", required_arg: "mondo", something: "else")
# default_arg: ciao
# required_arg: mondo
# other arg: something => else

# ArgumentError: missing keyword: required_arg
Written on January 25, 2018 by jasonschweier
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Git Shortlog

There are many ways to customize your git log output. However, the structure still the same: commit by commit.

A new variation I recently discovered was git shortlog. It displays commits by author, rather than most recently committed order. It is intended to help producing release notes.

This lets you find out who your largest contributors are, especially with the --summary option.

Try this:

$ git shortlog --summary | sort -r
Written on January 22, 2018 by jasonschweier
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Default Value for Deconstructed Object Parameter

In ES6, you can deconstruct a function’s object parameter to have its properties assigned to local named variables:

function MyComponent({
  item: { foo, bar }
}) { ... }

Also in ES6, the properties of the object parameter can have a default value set:

function MyComponent({
  item = "LOL"
}) { ... }

TIL: The object parameter can have both destructuring and default values applied to it!

function MyComponent({
  item: { foo, bar } = { foo: 1, bar: 2 }
}) { ... }
Written on January 19, 2018 by evanbrodie
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Debug Arrow Functions With Comma Operator

Use the Comma Operator to execute many JavaScript expressions in one ‘location’, but only return the value from the last expression.

This is commonly used in classic for loops, but has an interesting use case to quickly debug a single-line arrow function. For example, suppose you wanted to throw a console.log() into this function:

const myFunc = value => doCrazyOperation(;

Without the comma operator, this function would have to be expanded into a multi-line “block” function with a return statement, which is relatively quite longer:

const myFunc = (value) {
  console.log("value", value);
  return doCrazyOperation(;

With the Comma Operator, this debugging is much easier to write and maintain:

const myFunc = value => (console.log("value", value), doCrazyOperation(;
Written on January 19, 2018 by evanbrodie
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Using module_function instead of extend self

It’s a common pattern to use extend self inside ruby module to make all methods available in a static context/declared as class methods.

Instead of this, you can use module_function instead which will do the same as extend self but also have the added benefit of making those method private instance methods when they are included in another file.

module UserNameFormatter

  def format_name(user)

class User
  include UserNameFormatter

  def something
Written on January 19, 2018 by jordanneville
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Searching Through Gems

Sometimes you need to peak at the source of a class or method of a gem from your Gemfile. Since gems are managed by bundler, it has a command-line option that can help.

bundle show --paths will list the paths of all the gems from your Gemfile. You can grep through these directories to search.

I’m currently using ripgrep for searching at the command line, so can pass the paths there.

Here’s it all together in a simple Bash function:

function bundle-search() {
	rg $1 `bundle show --paths`
Written on January 17, 2018 by jasonschweier
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Enumerable Predicate Methods Have a New Argument

Enumerable#grep accepts an argument that returns elements that are true using case equality (===). These elements can then be passed to its block for further proccessing:

fruits = %w(apples orange grapes)
fruits.grep(/s$/) # => ["apples", "grapes"]
fruits.grep(/s$/) { |e| e.start_with?("a") } # => [true, false]

In Ruby 2.5, this parameter argument was added to the Enumerable predicate methods all?, none?, one?, and any?.

fruits = %w(apples orange grapes)
fruit.any?(/s$/) # => true

# === works with more than Regexes!
[1, 3.14, 2ri].all?(Numeric) # => true
[0, 1, 2, 3].all?(1..10) # => false
[0, 5].one?(1..3) # => false
[0, 5].none?(1..3) # => true
Written on January 15, 2018 by jasonschweier
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More Expressive Regular Expressions with Ruby

I came across some parsing code that contained this regular expression:

# the first capture is the left quote
# the second capture is the string content
# the third capture is the right quote
METHOD_CAPTURE = /Module\.method\(\s*(['"])(.+?)(['"])\s*\)/

This regexp is matching the string contents of a particular method call. It captures three pieces of information, mentioned in the comments.

This code is not self-documenting. We have three comments explaining the captures, and a regexp we must parse in wetware.

Furthermore, numerical indexes are difficult to track and modify in complicated regexps. PCRE supports named captures; denoted in Ruby by (?<name>pattern).

To make the comments superfluous, let’s refactor using the following:

  1. Use named capture groups
  2. Use interpolation to give descriptive names to common components
  3. Don’t capture needlessly (in our case, the captured quote characters are not used)
  4. Prefer [] over escaping (personal preference)
quote_character = %q|['"]|
optional_whitespace = "\s*"

METHOD_CAPTURE = /Module[.]method[(]#{optional_whitespace}#{quote_character}(?<string_contents>.+?)#{quote_character}#{optional_whitespace}[)]/

# #match returns an object or nil
matches = 'Module.method("some string")'.match(METHOD_CAPTURE)

# if an object, access captures by name:
matches[:string_contents] # "some string"

You can tailor how many named expressions/variables to use based on the complexity of the regexp.

Written on November 28, 2017 by jasonschweier
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Copy current file path relative to project root

I already knew about copying the current file path to the clipboard by using Shift+Cmd+C . The problem with this approach is that it copies the absolute path, for example, /Users/arturo/src/cool_project/lib/module/my_file.rb. This is not ideal if you are planning on sending this path to someone else or for some document you are writing.

A better option is to use RubyMine’s Action Copy Reference which by default is bound to Shift+Alt+Cmd+C. This copies the current file path relative to the project, for example, lib/module/my_file.rb

To summarize:

Copy Paths Action

  • Default shortcut: Shift+Cmd+C
  • Example text to clipboard: /Users/arturo/src/cool_project/lib/module/my_file.rb

Copy Reference Action

  • Default shortcut: Shift+Alt+Cmd+C
  • Example text to clipboard: lib/module/my_file.rb

Thanks to Jordan N. for the tip!

Written on November 27, 2017 by arturopie
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Force push safely using --force-with-lease

We periodically force push feature branches when we rebase them.

To do this safely, I first check manually to see if my pair has pushed any commits I don’t yet have in my local branch.

But there’s an easier and safer way to do this. The --force-with-lease option will fail if there are upstream changes not yet merged.

It will work smoothly for standard rebasing situations, but protect against any inadvertent destructive force pushes.

Thanks to Jason K for sharing this tip with me!

Written on November 14, 2017 by bryanmacdiarmid
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How to Center Vertically and Horizontally in CSS

This helpful guide teaches you everything you wanted to know about centering your HTML elements vertically and horizontally using CSS:

Written on October 24, 2017 by evanbrodie
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Regexes are supported by Capybara has_content?


I am trying to assert the presence of a button on the page by checking the button text:

expect(page).to have_content("Close")

Unfortunately, the page also has a dropdown that contains the option Closed.


Regex to the rescue!

expect(page).to have_content(/Close\b/)

Written on October 4, 2017 by clemenspark
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Finding Where a Method is Defined

One great thing about Ruby is how flexible it is. Although sometimes it can be hard to determine where a method definition comes from.

One useful technique to pull out in just this circumstance is the source_location method.

For example, suppose you see a call to the quantity method in a spec and you wonder where its definition comes from. Do some puts debugging by adding this line:

puts method(:quantity).source_location
Written on October 3, 2017 by alistairmckinnell
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Send commands to all panes in iTerm


I just edited my shell profile (~/.zshrc). Now I need to remember to reload any pane that needs the changes.


Send commands to all panes:

  1. Cmd + Shift + I
  2. source ~/.zshrc


Written on September 16, 2017 by clemenspark
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Lambda argument passing shorthand

Suppose that I have a Ruby lambda like so:

greeting = -> name { "Hello #{name}" }

The conventional way of calling this lambda is like so:"Ned") # "Hello Ned"

However, for those of you dreading having to type in call (hello, JavaScript developers), you can use this syntactic sugar instead:




I am now a sad panda to learn that this shorthand syntax is not recommended in the ruby-style-guide:

It’s still a cool learning for me to know that this syntax exists in the first place, though.

Written on September 14, 2017 by evanbrodie
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Repeat last substitution in VIM

Use the & motion to repeat the last substitution in VIM. IE, the most recent :s command.

Very handy in a git interactive rebase that requires every commit message to have a ticket reference changed.

Written on September 8, 2017 by evanbrodie
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FactoryGirl identifiers as symbols not strings

Why is FactoryGirl.create(:my_object) better than FactoryGirl.create("my_object")?

Symbols are immutable objects that are stored by the Ruby interpreter as a numeric ID (an implementation detail, the design of Ruby is flexible for different storage mechanisms).

Strings, on the other hand, take up a memory footprint as large as the number of characters in the string. Using symbols will thus take up less memory and potentially be faster because the same address in memory will be used.

If you have n instances of the same string in your code, Ruby will use O(n) memory to store all those strings, however, if you have n instances of the same symbol in your code, Ruby will use O(1) memory to do the same lookup.

Further reading:

This TIL came courtesy of a discussion with Evan and later on Arturo about best practices in writing test code, but shared here because it’s broadly applicable and the FactoryGirl example is just one use case.

Written on August 22, 2017 by jasonkurian
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Z-Index Equivalent in SVG

To mimic the z-index CSS property in SVG, add the SVG elements to the page in the reverse order that you expect their z-positioning to be set. The subsequent elements added are placed on top of previous elements.

For example, if I were using the React SVG charting library Victory and I wanted my chart lines to be stacked on top of my chart area shading, I will add them to my component like so:

  <VictoryArea ... />
  <VictoryLine ... />
Written on August 10, 2017 by evanbrodie
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Combine all ES6 generator values into an array

The ES6 spread operator can be applied to an iterable to combine all its results into one single array. A trivial use case for this is to merge extra elements into an existing array (ie, [...existingArray, 2, 3]).

This usage of the spread can be applied to a Generator to combine all the results of the calls to next() into one array. This serves as syntactic sugar to replace needing to use a for-of loop to do the same operation. Here’s an example (illustrative purposes only, ignore that this is not the best way to solve this problem):

function* evenNumbersGenerator(maxNum) {
  for (let i = 0; i <= maxNum; i += 1) {
    if (i % 2 == 0) {
      yield i;


const evenNumbersTo100 = [...evenNumbersGenerator(100)];

Side Learning: Generator functions cannot be declared as an arrow function, because they have to be declared as a “non-method function”.

Written on August 9, 2017 by evanbrodie
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Surround around array of React SVG components

It is a typical practice when writing a React component that renders a list/array of components to surround these components around a <div> tag. This is because React does not directly support rendering arrays of components.

This practice will not work if the React components will deep-render SVG elements instead of HTML markup. The solution instead will be to wrap the array of SVG-based child components around <g> tags (which stands for group in SVG).

Written on August 3, 2017 by evanbrodie
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VIM: Move a numbered line to current cursor

Let’s say I’m on line 20 and I want to move line 10 to my current line. Useful for code refactoring.

How I used to do it




The new way I’ll do it

Thanks to my learnings here:

:10m .
Written on June 21, 2017 by evanbrodie
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Exclusion using File Masks

When using “Find in Path..” functionality to find a word across multiple files, file masks can be used to match certain types of files. For example, using *.rb will only look through Ruby files. On the other hand, if you want to exclude Ruby files instead, you can add an ! at the front (i.e. !*.rb).

Here are other useful examples/combinations:

all files excluding spec tests: !*spec.rb

all Ruby files excluding spec tests: *.rb,!*spec.rb

Written on June 20, 2017 by joneriksuero
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Add have_selector() matcher to RSpec Request Specs

If you are used to writing controller specs, you are probably comfortable with the `have_selector matcher. However, in request specs this matcher is not available. By default, you can only do text search inside the request body which leads to brittle assertions.

You can add the have_selector matcher by updating your RSpec config to include the Capybara matchers on request specs as well.

RSpec.configure do |config|

config.include Capybara::RSpecMatchers, type: :request


Then you can write more confident Request specs by using assertions like expect(response.body).to have_selector('ul li', text: 'List content here!')

Written on June 9, 2017 by jordanneville
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Stop a docker-compose container without removal

Suppose you need to stop your docker-compose container but you don’t want to remove the container. For example, this container runs your database, so removing the container would mean that you would also lose all your data.

Don’t use docker-compose down. This will remove your container and you will have rebuild your database from scratch. Sad panda.

Instead, use docker-compose stop. You can then restart the container and have all the data back that you had before.


Written on June 1, 2017 by evanbrodie
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Search DOM by selector in Chrome Inspector


I want to select a DOM element by CSS selector on my React-generated web page for debugging purposes. In this case, I am trying to test out CSS selectors to be used in my Capybara acceptance test.


Use jQuery NO, DON’T DO THAT!

A neat feature of the Chrome Web Inspector is that I can search an entire page by CSS Selector, without needing to litter my code with debugger statements. Just open up the Elements tab and then press CMD-F (on Mac) to open up a search bar. I can now type whatever CSS Selector that I want and view the results that match. I can quickly test different selectors out, so that I can verify that I am writing my Capybara test accurately.


Written on May 31, 2017 by evanbrodie
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An Improvement to the Behaviour of the Git Pager

First, capture your current git pager settings (in case you want to go back):

git config --list | grep core.pager

Second, configure your new and improved git pager settings:

git config --global core.pager "less $LESS --tabs=2 -RFX"
--tabs=2: Is just right for displaying Ruby diffs

-R: Repaint the screen, discarding any buffered input
-F: Causes less to exit if a file is less than one screens worth of data
-X: Leave file contents on screen when less exits.

If you want to get even fancier consider diff-so-fancy.

Written on May 19, 2017 by alistairmckinnell
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Bulk Upsert through PostgreSQL 9.5+

Warning: This only works for PostgreSQL 9.5+ ___

Given the following:

  1. a users table:
    • id
    • name
    • created_at
    • updated_at
  2. users table only has 1 user with values:
    • id: 1
    • name: Alejandro
    • created_at: ‘2010-10-10 10:00:00.000000’
    • updated_at: ‘2010-10-10 10:00:00.000000’

You can upsert using the following SQL query:

  users(id, name, created_at, updated_at)
  (1, 'Alexander', NOW(), NOW()),
  (2, 'Belle', NOW(), NOW())


  1. User(id=1) will be renamed from Alejandro to Alexander. The updated_at value will be set to current time.
  2. User(id=2) will be inserted to users table with name = Belle, and both created_at and updated_at will be set to current time.
Written on May 11, 2017 by joneriksuero
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Chrome: Inspecting DOM elements that require focus

Using Chrome Dev Tools, I occasionally want to inspect an element that requires focus - for example, inspecting a selected date in a date selector.


As soon as I click the dev tools window, the element loses focus and I can no longer inspect in with the desired state.

Undesirable solution

On occasion when I’ve run into this scenario, I’ve placed a breakpoint or debugger statement in the JavaScript function that would be called when focus is lost. The problem with this is that it takes time and I need to locate the appropriate place in code.

Better solution

When in the desired state - for example, with the current date selected - pressing F8 will pause JavaScript execution. I can then inspect the DOM in the desired state.

Written on May 10, 2017 by bryanmacdiarmid
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Changing Your iterm2 Profile Programmatically

Change your iterm2 profile to Production with this command:

echo -e\033]50;SetProfile=Production\a

Create a function to make it easier to switch profiles:

function iterm_profile {
  if [[ -z $1 ]]; then

  echo -e "\033]50;SetProfile=$profile\a"

I use this feature to let me know I am working on the Rails migration.


Written on May 3, 2017 by alistairmckinnell
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Diff CSVs With Ease

We’re all familiar with diff tools like RubyMine, vimdiff, or the good old diff command. These work well for source code but are not optimal for CSVs files, which may have many columns and rows.

I found myself wanting to write CSV-specific diff tool, but I fought that Not Invented Here impulse and Googled first. I found a good Python library called csvdiff.

Imagine we have the following CSV file:

1,Alan Turing
2,John McCarthy
3,Edger Djikstra

We want to compare it to another file:

1,Alan Turing
3,Edsger Dijkstra
4,John Von Neumann

We’ve removed, edited, and added a row. The summary option confirms our changes:

$ csvdiff --style=summary id one.csv two.csv
1 rows removed (33.3%)
1 rows added (33.3%)
1 rows changed (33.3%)

The detailed view gives us all the gory details:

$ csvdiff --style=pretty id one.csv two.csv
  "_index": [
  "added": [
      "id": "4",
      "name": "Jon Von Neumann"
  "changed": [
      "fields": {
        "name": {
          "from": "Edger Djikstra",
          "to": "Edsger Dijkstra"
      "key": [
  "removed": [
      "id": "2",
      "name": "John McCarthy"
Written on April 27, 2017 by jasonschweier
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Range prefix to VIM command (from current line)

When I want to execute a command in VIM over a range of lines (for example, search-replace with :s) starting from the current line, I could execute a command like so:


This reads as search-replace from the current line (.) until 10 lines after. While useful functionality, it does require quite a bit of typing to execute.

Thankfully, there is a neat little shortcut that can be used to reduce some of this type. Simply enter the number of lines that you want to change from the current line and VIM will fill in the rest in the command prompt.

For example, I need to type 11: and VIM will insert :.,.+10 into the command prompt. You can now finish off this command like needed. Do note that the line count includes the current line itself (think of this count as current line plus number of lines after).

Written on April 23, 2017 by evanbrodie
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Squish Those Strings

While reading some Rails code, I came across a deprecation warning:

  `redirect_to :back` is deprecated and will be removed from Rails 5.1.
  Please use `redirect_back(fallback_location: fallback_location)` where
  `fallback_location` represents the location to use if the request has
  no HTTP referer information.

What caught my eye was the squish method on the heredoc. It’s common to see methods after heredocs to clean up formatting, but squish is a great method name.

squish removes all leading and trailing whitespace, then replaces all consecutive whitespace with a single space. One application has been cleaning up long string messages that use the line continuation operator. The community style guide says to only use line continuations for concatenating strings, but I think squish is cleaner:

long_string = "a long string " \
              "spanning " \
              "three lines"
# => "a long string spanning three lines"

better_long_string = "a long string
                      squished to a single line
                      without extra spaces or backslashes".squish
# => "a long string squished to a single line without extra spaces or backslashes"

An all-too-common caveat: squish is an extenstion method from active_support.

Written on April 20, 2017 by jasonschweier
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Speed Up Bundler

It turns out that you can speed up Bundler if you increase parallelization.

$ bundle config --global jobs 8

On OS X you can use the sysctl command to determine the jobs setting appropriate for your hardware:

$ sysctl hw.ncpu
hw.ncpu: 4

I’m using number of cores times two. Works for me. YMMV.

Written on April 20, 2017 by alistairmckinnell
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Cherry-picking a range of commits in git


I would like to cherry-pick a range of commits (e.g. an entire branch). For example, I want to cherry-pick the commits f00b4r to f00ba5, where foob4r is the oldest commit on the branch.


git cherry-pick f00b4r~..f00ba5.

Written on April 19, 2017 by ryandevilla
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Using Trigram Indexes to Speed Up LIKE Queries

Queries containing ILIKE '%anything%' result in table scans since they have a leading wildcard. Typical btree indexes can not help improve performance in this case.

Trigrams are 3-character slices of words:

SELECT show_trgm('Ruby');
-- {"  r"," ru","by ",rub,uby}

They are useful as indexes since they can speed up LIKE, ILIKE, ~, and ~* clauses.

Let’s query a table of 14K email addresses:

CREATE TABLE emails (email TEXT);

\copy emails FROM 'emails.csv' DELIMITER ',' CSV;


The query plan shows a table scan:

Seq Scan on emails
  Filter: (email ~~* '%ion%'::text)
  Rows Removed by Filter: 14040

with an average execution time of 15ms. Let’s create a trigram index and try again:

-- postgres 9.2+

CREATE INDEX emails_search_email_idx ON emails USING GIN (email gin_trgm_ops);


The improved query plan is:

Bitmap Heap Scan on emails
  Recheck Cond: (email ~~* '%ion%'::text)
  Heap Blocks: exact=98
    -> Bitmap Index Scan on emails_search_email_idx
       Index Cond: (email ~~* '%ion%'::text)

and averages 0.8ms. A 19X improvement without updating any SQL queries! YMMV

Written on April 16, 2017 by jasonschweier
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bundle update --conservative

Let’s say you want to update the gem foo. After running bundle update foo you look at your gemfile.lock and find that not only was foo updated, but so were many of its dependencies. You also notice that many of these dependency updates weren’t necessary, as the previously installed versions were compatible with the new version of foo.

The default bundle update foo behaviour will unlock and update all dependencies of foo.

If you don’t want to update these dependencies unnecessarily, one solution is to add the current versions to your gemfile.lock.

However, an easier way to prevent the updating of shared dependencies is to use bundler’s new --conservative flag.

Written on April 13, 2017 by bryanmacdiarmid
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All the different ways to lock your Mac computer

  • Using the keyboard: CTRL-SHIFT-eject
  • Using Alfred: execute the lock command
  • Using a taskbar icon from Keychain:
    • Open the app Keychain Access
    • Preferences –> Enable the option “Show keychain status in menu bar”
    • A lock-shaped icon will appear in the taskbar, with the option “Lock Screen”
  • Use Hot Corners:
    • System Preferences –> Desktop & Screen Saver –> Hot Corners button
    • Set one of the corners as “Put Display to Sleep”
    • Mouse into the direction of that corner (on the monitor closest to that side, for multi-monitor setups)
  • If all else fails, just hold the Power button on your keyboard for a second to put your computer to sleep
Written on April 12, 2017 by evanbrodie
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Chef override attributes vs chef-client -j switch

When applying recipes via chef-client, you can override attributes via the –json-attributes (or -j) switch. However, the override_attributes option on roles, environments and recipes has higher precedence over the –json-attributes switch.

For more info about Chef attribute precedence, use this as a reference. The attributes set via --json-attributes are “normal” attribute types.

Written on April 7, 2017 by arturopie
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async/await Keywords of ES7 for Simpler Promises

ES7 introduces the async/await keywords. They are mostly syntactic sugar on top of Promises. You can write cleaner more readable asynchronous tasks code.

NOTE: They are available in Node 7.6.0 also.


Here is some code for programmatically creating a coding exercise for a developer candidate that has applied to us. We’ve improved the readability of it using async/await.

This hard to read test which uses Promises:

it('returns any errors that may have occurred', () => {
  return automator
    .then(repo => !repo ? automator.createExercise() : Promise.resolve())
    .then(() =>'alice', `hubot create coding exercise repo for ${candidateEmail}`))
    .then(() => {
      expect(lastBotMessage()).to.contain(`Error creating coding exercise for *${candidateEmail}*:`)

Becomes this:

it('returns any errors that may have occurred', async() => {
  let repo = await automator.getRepo();
  if (!repo) {
    await automator.createExercise();

  await'alice', `hubot create coding exercise repo for ${candidateEmail}`);

  expect(lastBotMessage()).to.contain(`Error creating coding exercise for *${candidateEmail}*:`)

Which reads more like an Arrange/Act/Assert style test.

Written on March 28, 2017 by shahriyarnasir
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Use PostgreSQL table as queue skipping locked rows

This command only works in PG 9.5

First, are you sure you shouldn’t be using some in-memory queue? Or some message broker? Or Redis?

If you are really convinced that you want this sort of behaviour on top of the goo’old PostgreSQL you can achieve a queue-like access pattern by locking and skipping locked rows.

One way to ensure that only one database client can modify a set of rows is to select the rows for update as in


This will block any other UPDATE or SELECT .. FOR UPDATE until the above transaction is finished. Now if you want concurrent database clients to fetch the next row available in the priority list just use:


The above command could be interpreted as “select the next row from queue that nobody has yet locked”.

Written on March 22, 2017 by diogobiazus
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Skip duplicate history entries in zsh

In zsh, pressing UP searches through the history and brings up all matching commands, even if they are duplicates. That means, sometimes you need to press UP many times to actually find a previous match.

However, it is possible to disable this behaviour and skip duplicate entries from the history. To do that, add one line to your ~/.zshrc:

Written on March 22, 2017 by maksimbezsaznyj
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Ignore whitespace-only changes in Gitlab MRs


You are reviewing a Gitlab Merge Request (MR). It involes changes where a Ruby file is moved into or out of particular modules. This means that one or more module ... end constructs are either added or removed around the entire class, resulting in a tabbing-width change on almost every line of the file. This makes reviewing the file in the MR quite difficult, as the reviewer will need to sift through the code diff and separate out actual logic changes from whitespace-only changes.


By appending ?w=1 to the end of the URL of the MR, Gitlab will ignore all lines that only feature a whitespace change in the code diff. This means that the only changes visible will be ones with a non-whitespace change, thus allowing the reviewer to focus in on actual logic changes and not waste time reading whitespace changes.

Time to poke Gitlab EE support on this issue:

Written on March 22, 2017 by evanbrodie
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Assignment on associations will bypass validation

Important gotcha that assignment to has_many associations will cause an immediate save even if callback validation fails.

u = User.last

u.accounts = [] # returns false because this user cannot have blank accounts

u.reload.accounts # returns empty array

The gotcha here is that save is a no-op really. As soon as u.accounts=[] is called, the data is saved immediately, bypassing validation.

Written on March 22, 2017 by jordanneville
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Fixing ZDT Deploys with Monitoring-Driven Develop.

We were debugging a bug in our zero downtime deploy script. We tested the deploy using Chef, Kitchen and Vagrant. The bug was causing an error page to show for less than 3 seconds at the very end of the deploy.

We used Monitoring Driven Development to consistently reproduce the bug (the red phase), and to validate our fix (the green phase). Here were the steps:


  1. kitchen login # ssh to the vagrant box
  2. sudo tail -fn100 /var/log/nginx/go.access.log # to see the response codes from the server. If all responses show 200 code during the deploy, the deploy is working.
  3. Open other terminal window
  4. kitchen login # ssh to the vagrant box
  5. watch -n 1 "curl localhost" # make a request every 1 second

Then we followed this feedback loop

On the host computer:

  1. Make changes to the deploy recipe
  2. kitchen converge # this will run our deploy
  3. Check the output of the logs to see the result of the changes
  4. Repeat the loop until bug is fixed
Written on March 18, 2017 by arturopie
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Creating multiple objects with Factory Girl

If you need to create more than one object from a factory, you can use the create_list method to accomplish this.

FactoryGirl.create_list(:user, 10, :supervisor)

Will create 10 supervisor users with the supervisor trait.

Written on March 15, 2017 by jordanneville
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Replacing with


I want to create an array containing objects created with an incrementing integer index parameter. For example, an array of hashes containing strings built off of the incrementing number.

Standard Solution

my_array = do |index|

BUT…rubocop didn’t like this:

… C: Performance/TimesMap: Use with a block instead of

Improved Solution

The improved solution allows us to build the same array with less chained methods, thus improving readability:

my_array = do |index|
Written on March 13, 2017 by evanbrodie
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pgcli — a great alternative to psql

Ever wished for a feature-rich, intuitive command-line postgresql client? Look no further! Presenting, pgcli — a result of pouring creativity into features rather than the name of the tool.


  • Smart autocompletion for almost anything. Even column names in the select query are properly autocompleted from the table you are selecting from;
  • Multi-line query editing support;
  • SQL Syntax highlighting;
  • CLI parameters compatible with psql params. No need to relearn anything;
  • Vi mode, allowing to edit multi-line queries using some of the vi bindings. There are also Emacs bindings too;
  • Installation as easy as pip install pgcli (and if that fails, fix is as easy as xcode-select --install (usually));

Grab your copy today!

Written on March 9, 2017 by maksimbezsaznyj
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Speeding Up Rake Command Completion

The speed of rake command completion is determined by the startup time of your Rails app.

If your Rails app is slow to startup, the oh-my-zsh rake-fast plugin will make rake command completion tolerable again.

Edit your zsh configuration file:

plugins=(... rake-fast ...)

After refreshing your shell instance issue the following command:

$ rake_refresh

Take a deep breath. Enjoy fast rake command completion.

Written on March 6, 2017 by alistairmckinnell
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OS X Command Line

I love being able to use Alfred as a kind of GUI command line…

..and I also like using the command line to get things done. I just discovered all sorts of new things that I can do from the command line from this GitHub repo.

For example, to show Wi-Fi Connection History:

defaults read \
  /Library/Preferences/SystemConfiguration/ | \
  grep LastConnected -A 7
Written on March 4, 2017 by alistairmckinnell
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Record File Handle Usage in OSX

lsof is a helpful tool for looking at what files a process currently has open, however sometimes a process may only access a file for a second and lsof may miss the moment.

For OSX we also have Instruments. This is included with XCode and is pretty straight forward to use:

  • Open Instruments
  • Select File Activity
  • Select the process
  • Hit Record
  • Perform your action
  • Stop Recording

You can also save the log for later analysis.

Written on March 3, 2017 by adamkerr
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Mocha: Fail on any console error message


I want to write a Mocha (JS) test that will fail if there is any warning printed to the console to fail. My use case to necessitate this requirement is that I want to test whether the correct prop type is passed to a React component. PropTypes exists for this purpose, but would only print out a message to the console instead of failing.


Use the following code, either at the beginning of your test file or a global helper such as specHelper.js, to stub out the implementation of console.error to throw an Error and thus fail the test.

before(() => stub(console, "error", (warning) => {
  throw new Error(warning);

after(() => console.error.restore());

Reference: this gist.

Written on February 24, 2017 by evanbrodie
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webpack-merge is a thing and it is beautiful

Let’s say you want to redefine a loader from your base webpack config in your production webpack config. Try !


const config = {
  entry: "./index.js",
  module: {
    rules: [
        test: /\.css?$/,
        exclude: /node_modules/,
        use: [{
          loader: "css-loader",
          options: { sourceMap: true }, // set to true
        test: /\.css?$/,
        include: /node_modules/,
        use: ["css-loader"],


const merge = require("webpack-merge");
const baseConfig = require("webpack.base.config");

const productionConfig = {
  module: {
    rules: [{
      test: /\.css?$/,
      exclude: /node_modules/,
      use: [{
        loader: "css-loader",
        options: { sourceMap: false }, // override to false

module.exports =, productionConfig);


const config = {
  entry: "./index.js",
  module: {
    rules: [
        test: /\.css?$/,
        exclude: /node_modules/,
        use: [{
          loader: "css-loader",
          options: { sourceMap: false }, // yep! it's false
        test: /\.css?$/, // but we didn't touch this rule
        include: /node_modules/,
        use: ["css-loader"],
    ], // and we didn't append anything either!
}; is aware of the shape of a webpack configuration and allows you to update only the rule you want.

Check it out:

Written on February 24, 2017 by nedschwartz
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Capybara will skip invisible elements by default

While working on an acceptance test for a date range filter in GO, we were having an issue where Capybara couldn’t find an element on the page, even though we could verify it was there. Eventually we realized that the element had an opacity of 0, and that Capybara was passing it over. To illustrate, imagine you have an element with the id #myElement.


#myElement { opacity: 0; }

And in your Rails spec:


The spec will fail, because #myElement can’t be found.

Fortunately, there is a visible option that can be set to false so that Capybara doesn’t skip the element. So now, changing the line in the spec to:

page.find("#myElement", visible: false);

will cause it to pass.

Written on February 24, 2017 by jerridanquiring
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Encrypt data using psql + keybase

To export any query to a CSV and send it to stdout one can use:

psql -c "\copy (select version()) to stdout csv header"

So you can just replace select version() with any query in the above command and the results will be dumped in your terminal screen. If you have any sensitive data that is not already encrypted you could pipe this results directly to keybase as in:

psql -c "\copy (select version()) to stdout csv header" | keybase encrypt diogob

Where diogob is the recipient of your message (or your own username in case you want to store this file for future use).

Written on February 17, 2017 by diogobiazus
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Creating More than One Instance with FactoryGirl

In some test fixtures I need to create an array of instances . FactoryGirl provides the create_list method for exactly this purpose.

To create four shipments on an outbound trailer:

FactoryGirl.create_list(:shipment, 4, outbound_trailer: trailer)

In the example above, create_list returns an array containing the newly created shipments.

Written on February 12, 2017 by alistairmckinnell
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Global gitignore

To enable a global .gitignore for a specific user you can use the git config core.excludefiles as in:

git config --global core.excludesfile '~/.gitignore'

This will make the .gitignore in your home folder to be used in every git project in adition to local .gitignore files.

For more info read the git documentation on gitignore

Written on February 7, 2017 by diogobiazus
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While optimizing calls to a recursive table, we found a neat SQL solution. It uses a common table expression as a working table to query against iteratively.

Here’s an example of using WITH RECURSIVE with a modified nested set example of clothing categories that find all paths through the categories:

CREATE TEMPORARY TABLE categories (id INT, name text, parent_category_id INT);

  (1, 'Clothing', null),
  (2, 'Mens''s', 1),
  (3, 'Women''s', 1),
  (4, 'Suits', 2),
  (5, 'Dresses', 3),
  (6, 'Skirts', 3),
  (7, 'Jackets', 4),
  (8, 'Evening Gowns', 5);
WITH RECURSIVE category_hierarchies AS
(SELECT id, parent_category_id, name AS full_path
 FROM categories
 WHERE parent_category_id is NULL


        parent_categories.full_path || ' -> ' || as full_path
 FROM categories AS child_categories
 INNER JOIN category_hierarchies AS parent_categories
   ON child_categories.parent_category_id =
SELECT full_path FROM category_hierarchies ORDER BY full_path;

Produces paths through all categories:

  • Clothing
  • Clothing -> Mens’s
  • Clothing -> Mens’s -> Suits
  • Clothing -> Mens’s -> Suits -> Jackets
  • Clothing -> Women’s
  • Clothing -> Women’s -> Dresses
  • Clothing -> Women’s -> Dresses -> Evening Gowns
  • Clothing -> Women’s -> Skirts

Read more about WITH RECURSIVE queries

Written on February 7, 2017 by jasonschweier
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Run last command in BASh/ZSH (they're different)

To run the last executed command in BASH, execute the following:


In ZSH, things are a little different. Using !! will only expand the command into the shell prompt. You would have to press enter again to execute it. Rather, if you want to immediately execute the last command similar to BASH, use this:


If you prefer for ZSH behaviour to match that of BASH, then add setopt no_hist_verify to your .zshrc file.

Written on February 3, 2017 by evanbrodie
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Serializing many value objects to database columns

While reading the IDDD book on serialization of value objects there is this description of an approach called “ORM and Many Values Serialized into a Single Column”. It’s good to note that some of the main objections to this approach are technology related and barely applicable in a world of Rails’ ActiveRecord + PostgreSQL.

The objections presented by the book are:

  • Column width: It mentions that serializing to varchar fields will meet some limitations imposed by Oracle and MySQL implementations. In PostgreSQL, besides having composite types (e.g. json or array), the limit on any column is much higher (1GB).
  • Must query: The book states that if the values must be queried this approach cannot be used. This is another limitation imposed by the underlying technology. Using PostgreSQL one can easily query composite values and even created indexes over them.
  • Requires custom user type: This is not related to the database technology but is heavily biased towards hibernate. In Rails’ ActiveRecord the custom serializers require very little boilerplate and it offers out of the box support for json, array and range types.
Written on February 2, 2017 by diogobiazus
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Am I executing the correct executable?

Q: When I run a command (let’s say rails), which executable is it executing?


> which rails

Q: Ah, I see which one it’s running. And it’s not the right one! Where are all the potential executables, given the current PATH?


> where rails

Now I know whether it’s a PATH ordering issue, or whether it’s not included PATH at all.

Written on January 31, 2017 by clemenspark
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Turn AWS tags into a useful data structure with jq

The JSON responses from the AWS API contain tags in a data structure like this:

"Tags": [
        "Value": "consul-test-jf",
        "Key": "Name"
        "Value": "test-jf",
        "Key": "consul-group"
        "Value": "server",
        "Key": "consul-role"

This structure is awkward to query with jq, but you can map it into a normal object like this:

jq '<path to Tags> | map({"key": .Key, "value": .Value}) | from_entries'

Which returns an object that looks like this:

  "consul-role": "server",
  "consul-group": "test-jf",
  "Name": "consul-test-jf"
Written on January 27, 2017 by justinfitzsimmons
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Comparing Version Strings in Ruby

While writing a Ruby script, I needed to check the the version of a binary dependancy. The --version switch gets me the data, but how to compare to the required version?

The binary follows semver, so a quick and dirty attempt might be:

"1.4.2".gsub(".", "") >= "1.3.1".gsub(".", "")
# => true

Unfortunately, this is misleading: we are lexicographically comparing the strings and these strings happen to have the same length. Thus, "142" comes after "131".

Testing that version "1.200.0" is newer than "1.9.0" will fail as "120" comes before "190".

It would be straight-forward to write a small class to parse the string and compare the major, minor, and patch values. But, Ruby has a quick solution provided by RubyGems. Since Ruby 1.9, RubyGems has been included in Ruby’s standard library:"1.200.1") >="1.3.1")
# => true

Gem also provides a way handle pessimistic constraints:

dependency ="", "~> 1.3.1")
dependency.match?("", "1.3.9")
# => true
dependency.match?("", "1.4.1")
# => false
Written on January 26, 2017 by jasonschweier
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Configuring a Rails app to redirect http to https


I have a Rails app on Heroku that is serving up a site on http and https. Google oAuth’s callback URL is for https, so attempting to log into the site from the http URL fails.


The intention was to serve up the site just from the https url, so the solution is to configure Rails to redirect all http traffic to https.

In config/production.rb:

  config.force_ssl = true


Written on January 25, 2017 by clemenspark
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Decorator Pattern in Ruby with SimpleDelegator

The Decorator Pattern allows us to chain new behaviours to objects without modifying the underlying objects. It is an application of the Open/Closed Principle. This pattern is useful for example when we need to tack on logging, monitoring, and other non-functional requirements to objects.

In Java or C# this can be achieved using interfaces. In Ruby, we can use the SimpleDelegator class to achieve this:

require "delegate"

class FooDecorator < SimpleDelegator
  def bar
    "This is a decorated #{}"

class Foo
  def bar

  def fiz

decorated =
puts # outputs "This is a decorated bar"
puts decorated.fiz # outputs "Fiz"

double_decorated =
puts # outputs "This is a decorated This is a decorated bar"


Written on January 24, 2017 by shahriyarnasir
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Bundle Console

bundle console [GROUP]

runs Ruby console with bundled gems

Written on January 23, 2017 by joneriksuero
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Non-Invasive Monitoring of Socket Traffic


I would like to diagnose failures to communicate with an external service over a network socket, without making modifications to the code or otherwise disturbing a production-like environment.


One writes to or reads from a socket by making a request to the kernel (a.k.a syscall). This requires the file descriptor (numerical identifier) of the socket and the message to be sent over the socket, or a buffer that will contain the next message read from the socket.

Using strace (or dtruss on MacOS), one can inspect the stream of syscalls issued to the kernel and the arguments for each syscall. First, find the ID of the process that will be communicating over the socket:

ryan@staging ~ $ ps ax | grep unicorn
99999 ?        Sl     0:00 unicorn worker[0]

Then attach to the process with strace:

ryan@staging ~ $ strace -p 99999
Process 99999 attached
[pid 99999] write(11, "Hello", 6) = 6
[pid 99999] read(11, 0xBAAAAAAD, 64) = -1 EAGAIN (Resource temporarily unavailable)

Here, a Hello message was sent with a write syscall over socket with file descriptor 11, though the read syscall failed as the socket was temporarily blocked.

Written on December 16, 2016 by ryandevilla
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Passing all env. variables to a shell command

Some of the methods in the Kernel module allows you to pass environment variables to a shell command. So rather than doing:

system("RAILS_ENV=test rake do_stuff")

You can do

system({ "RAILS_ENV" => "test" }, "rake do_stuff")  

This is particularly useful when we want to pass all environment variables on our current process.

system(ENV, "rake do_stuff")
Written on December 16, 2016 by arturopie
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Attach to Local Ruby Process with Debugger

RubyMine has a nice feature that allows you to debug a Rails app without restarting the server.

With the server running,

1) Run the “Attach to Local Process..” action from RubyMine

2) RubyMine will show a list of Ruby processes running. Pick the one running your server

3) Wait for RubyMine to connect to the process

4) Add a break point in RubyMine

5) Execute the action on the web application that hits that breakpoint

6) Execution will stop on that line. Now you can use all the nice tools the RubyMine debugger gives you.

I’m really exited with this new feature and I hope you are too. You can read more about it in here

Written on December 11, 2016 by arturopie
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Prefer sort_by to sort when providing a block

Prefer the sort_by method over the sort method whenever you provide a block to define the comparison.

Common form:

line_adds.sort { |x, y| x.elements["ItemRef/ListID"].text <=> 
  y.elements["ItemRef/ListID"].text }

Preferred form:

line_adds.sort_by { |x| x.elements["ItemRef/ListID"].text }

For small collections both techniques have similar performance profiles. When the sort key is something simple like an integer there is no performance benefit from sort_by.

The performance difference is especially noticeable if the sort key is expensive to compute and/or you have a large collection to sort.

The algorithm that yields the performance benefit is known as the Schwartzian Transform.

Written on December 11, 2016 by alistairmckinnell
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React will conditionally batch calls to setState()

React tries to be smart and batch calls to setState() when its being called from a UI event context (e.g. button click). This has ramifications on code as your setState() call is no longer synchronous and accessing this.state will actually refer to the old state.


this.state = { hello: false };
onClick() {
   this.setState({ hello: true });
   console.log(this.state.hello); //<=== will print false instead of true

However, if the setState is in a context not from a UI event, setState becomes synchronous

this.state = { hello: false };
changeState() {
   this.setState({ hello: true });
   console.log(this.state.hello); //<=== will print true!

There’s more info here on the topic of batching setState calls:

Written on December 7, 2016 by jordanneville
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Ruby print to replace contents on same line

In Ruby, the print command can be used with the '\r' (carriage return) character to bring the cursor back to the beginning of the printed line, so that the next print call will replace the contents already outputted to that line. This is a very useful tool for printing status updates in a CLI script. For example:

print "#{index} done. Progress: %.2f%" % (index.to_f / items * 100).round(2) + "\r" if (index % 10) == 0

This will print and replace a line in STDOUT to report the status of a list of items being processed by a function, like so:

200 done. Progress: 15%

Typewriters still hold a lasting impact on modern-day computing!

Written on November 23, 2016 by evanbrodie
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Hotkey to switch control mode in Mac Screen Share

I use MacOS screen sharing to power pair programming sessions that I have in my development team. There are two modes for the navigator to use when observing the driver’s screen (assuming that the screen being shared is of the driver): Observe Mode to disallow taking control of the screen, or a self-explanatory Control Mode.

I like being in Observe Mode as the navigator so that I don’t mistakingly take control of the driver’s screen and start polluting the screen with accidental key strokes. But if I ever need to switch control, I would have to then make a mouse click on the correct icon. This gets annoying if I am observing in Full Screen mode (which is almost always). I would have to exit full screen mode first in order to switch to taking control.

SOLUTION: I can instead use the CMD-ALT-X key combination to quickly switch control mode :D

Written on November 18, 2016 by evanbrodie
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Why Git Uses (:) to Delete Remote Branch

It would appear that the colon in git push origin :<branch-to-delete> is used exclusively to delete branches. But such is not the case.

The format for the refspec is*:


This tells Git to push the source branch to the destination branch in remote. So if the source is blank, we get a leading colon. This has the effect of deleting the destination branch. Its like saying “push null pointer to destination”.

*You can learn more about the refspec in its entirety in this Stack Overflow

Written on November 10, 2016 by shahriyarnasir
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Performance Metrics for Scripts Using Command Line

To quickly collect performance metrics for a script via command line:

  1. Start running the script. Make note of the process name that the script is running as (e.g. ruby)
  2. Create a script called with this content: ps aux | grep $1 | head -1 | awk '{print "CPU="$3 ", MEM="$4 ", RSS="$6}'
  3. Make the profiler executable: chmod +x
  4. Execute the profiler in a watch session every minute: watch -n 60 --no-title "./ SCRIPT_IDENTIFIER | tee -a logfile". Where the script identifier is any text that we can use to grep for the process in the ps aux output.
  5. After your script is done running or you have enough data points, observe the output in logfile.

NOTE: RSS is resident set size

Written on November 8, 2016 by shahriyarnasir
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ZDT Column Rename in a Distributed System

In order to deploy code to a highly available distributed system any two sequential versions of the code can be running at the same time. Therefore they need to be compatible.

  1. Add the new column, keep the columns in sync when updating.
  2. Migrate the data, start using the new column however fallback to the old column if the new column is blank, continue keeping the columns in sync.
  3. Remove all dependencies on the old column, only use the new column, do not sync them anymore.
  4. Drop the column.

When in Rails, Step #3 requires some special care as the column needs to be marked for removal:

module MarkColumnsForRemoval
  def mark_columns_for_removal(*columns_marked_for_removal)
    @columns_marked_for_removal =

  # Overrides ActiveRecord's list of the database columns in order to hide a column which we intend to delete
  # This ensures that ActiveRecord does not try to read or write to the column
  def columns
    cols = super
    cols.reject { |col| (@columns_marked_for_removal || []).include?( }

class SomeModel < ActiveRecord::Base
  # Remove this as part of step 4 when dropping the old_column
  extend MarkColumnsForRemoval
  mark_columns_for_removal :old_column
Written on October 31, 2016 by adamkerr
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A quick deep dive into 'rake gettext:find'


I am using Ruby Gettext to manage translations. But today, when I ran rake gettext:find to update my PO files, none of them got updated.


The Investigation

After some digging, I noticed that Ruby Gettext defines one FileTask (a specific type of Rake task) per PO file, which delegates the work to GNU gettext.

FileTask looks at the timestamps of dependent files, and only executes the supplied block if any of the dependent files have a timestamp later than the file to update.

For example:

dependent_files = ["translations_template_file.pot"]
file "file_to_update" => dependent_files do
  # update the file

Why gettext:find was not doing anything

It turned out that gettext uses two FileTasks.

One to update the template:

files_needing_translations = ["file1.js", "file2.rb"]
file "translations_template_file.pot" => files_needing_translations do
  # update the translations template file

and another to update the PO file:

file "en-US/translation_file.po" => ["translations_template_file.pot"] do
  # update "en-US/translations.po"

The reason gettext:find did not do anything was because none of the files needing translation were updated, thus no PO files were updated.


> touch one_of_the_files_that_gettext_looks_at.js
> rake gettext:find
Written on October 28, 2016 by clemenspark
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the .then(onSuccess, onError) anti-pattern


  function onSuccess (res) {
    // stuff happens, but oh no!
    // an error is thrown in here!
  function onError (err) {
    // request-only error handler


  .then(function onSuccess (res) {
    // stuff happens, but oh no!
    // an error is thrown in here!
  .catch(function onError (err) {
    // yay! The error thrown in the function above
    // can be handled here or rethrown to be handled elsewhere.

More details here.

Written on October 5, 2016 by jasonkurian
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Compounding expectations in Rspec and Chai

When I had multiple expectations on the same object in rspec, I would write the code like so:

expect(page).to have_content("Foo")
expect(page).to have_content("Bar")
expect(page).to have_content("Other Stuff")

You can save yourself some typing if you instead use compound expectations, which is basically the usage of the and function after the previous expectation. Doing so will allow the previous code to be writted as such:

expect(page).to have_content("Foo")
  .and have_content("Bar")
  .and have_content("Other Stuff")

The same concept also exists in the Chai JavaScript testing library (documentation):

  .and.contain("Other Stuff");
Written on October 5, 2016 by evanbrodie
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Add executable flags in git file

There is support in the git add command to make a file tracked in your git repository executable. For example, let’s say you added a script to your repo but forgot to add the executable bit to its file permissions. You can now do this:

git add --chmod=+x

One gotcha of this approach is that this will only change the permissions tracked by git, but not the actual permissions of the file on YOUR filesystem. You will still need to run chmod +x to modify your local permissions. However, your teammates should be able to pick up the permission changes from a git pull.

Courtesy of

Written on October 3, 2016 by evanbrodie
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ES2015 Arrow fns do not have the arguments object

const myFn = (/*unknown arity*/) => {
  console.log(arguments); //EMPTY ARRAY!
function myFn(/*unknown arity*/) {
  console.log(arguments); //returns what you expect!

My takeaway: only use arrow functions when they’re necessary, which actually isn’t that often! Plain old named JS functions are still powerful and if necessary can still easily be bound with .bind(this).

Related reading:

Written on September 29, 2016 by jasonkurian
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Matching array subset in Ruby


How do you evaluate whether one array is a subset of another? For example, are the elements ` [a,c] included in [a,b,c]`?

First attempt:

I was hoping to find something like ` Array.include?([…])`, but this only checks if the array includes the argument as one of its values.

Second attempt:

Another approach is to pass a block into ` Array.any?`

!arr1.any? { |e| !arr2.include?(e) }

But the double negation is rather indirect and doesn’t easily reveal the intent.

I considered extracting a method to name the functionality:

def subset?(arr1, arr2)
  !arr1.any? { |e| !arr2.include?(e) }

But it’s still difficult to read, as it’s not clear whether arr1 is a subset of arr2, or vice versa.

Final Solution:

The ` Enumerable module includes a to_set method to convert the array to set, and Set includes a subset?` method.


Technically, you need to require set.rb to get this method defined on Enumberable:

require "set"


But you get this require for free in Rails.

Written on September 14, 2016 by cameronwoloshyn
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Add extra line to git commit message from CLI

You can add extra lines to your commit messages by adding an extra -m flag to the git commit flag. This is useful if you have extra information that you want captured in your commit, but you don’t want it in your commit message header. For example:

git commit -am "Updates the README with copyright information" -m "This conforms to requirements from Legal."

Will produce the following commit message:

Updates the README with copyright information

This conforms to requirements from Legal.

Now your commit message is split up into a header and a body. You can also add another -m flag for a footer.

Written on September 12, 2016 by evanbrodie
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Rolling back Rails migrations

There are a bunch of ways to roll back migrations, so I figured I’d capture them in Q & A format.

Let’s say the following migration files exist:

> ls db/migrate


Q: How do I roll back the last migration.
A: rake db:rollback

Q: How do I roll back the last 3 migrations?
A: rake db:rollback STEP=3

Q: How do I roll back a specific migration?
A: rake db:migrate:down VERSION=20160615142814
The timestamp comes from the filename: 20160615142814_migration_3

and… the one I learned today:

Q: How do I roll back all the migration past a certain version?
A: rake db:migrate VERSION=20160615142814.
The above will keep the following:


and roll back the following:


In other words, it will keep all the migrations upto and including the version you specified.

Written on September 8, 2016 by clemenspark
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RSpec Matchers for Array Comparisons

Whenever you are matching arrays ask yourself two questions:

  • Is order important?
  • Am I matching a subset of the elements or all of the elements?

How I decide on a matcher:

  1. Choose between the eq and be matcher if order is important.
  2. Choose the include matcher if you want to match on a subset of the elements.
  3. Choose between the match_array and contain_exactly matcher if you want to match all elements (and order doesn’t matter).

Below is an example of an improvement to a previously intermittent test. I replaced the eq matcher with the match_array matcher because I wanted to match all location_ids and order doesn’t matter.

expect(location_ids).to eq([,])
expect(location_ids).to match_array([,])

The root cause of the intermittent test was that the locations were being retrieved from the database with no order specified. From the PostreSQL documentation: If sorting is not chosen, the rows will be returned in an unspecified order. The actual order in that case will depend on the scan and join plan types and the order on disk, but it must not be relied on.

Written on September 8, 2016 by alistairmckinnell
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Retrieving the IDs for a Model

Prefer the ids method to map(&:id) when you want to retrieve an array of model IDs.



In the example above, using ids avoids fetching the receive orders from the database.

Rails Source

def ids
  pluck primary_key
Written on August 25, 2016 by alistairmckinnell
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How to see invisible text in iTerm2

Yesterday, I tried to run ‘npm test’ for a new project and the text was invisible (i.e. the same color as the background color of my chosen color scheme for iTerm2). You can find a long discussion about this problem here:

Buried in this discussion was the solution: iTerm2 -> Preferences -> Profiles -> Colors -> Minimum contrast -> Move slider about a third of the way

Written on August 24, 2016 by jasoncheong-kee-you
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Testing an Independent Mixin With RSpec

Objective: write a spec for the Inventory::Query mixin.

Note: the mixin is independent of the including class as it does not depend on any instance variables or instance methods.

Original Approach

class InventoryQueryTest
  include Inventory::Query
subject(:inventory_query) { }

Preferred Approach

subject(:inventory_query) { ( { include Inventory::Query }).new }


Simpler and avoids polluting the global namespace with a test class.

Written on August 22, 2016 by alistairmckinnell
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NPM: List available custom scripts in the CLI

If you are working in the CLI on a project that uses NPM and you want to know what what custom scripts are available to you, without need to open and scroll through package.json, just simply execute:

npm run

and all your custom scripts will be outputed to the screen.

Written on August 16, 2016 by evanbrodie
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Toggle Console Tab From Chrome Inspect Tools

If you have the Inspect Tools open on your Google Chrome browser, you can toggle a Console tab to appear at the bottom of the Inspect pane by pressing Escape on your keyboard. This is very useful if you need to have another Inspect tab open at the same time as the Console, such as Source or React Dev Tools.

Written on August 15, 2016 by evanbrodie
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Prettify JSON in the browser console


I want to check the shape of data for an XHR request in Chrome. So I go to the Network panel in the inspector.

When I check the response tab, I see the following:


Not very inspectable.

When I check the preview tab, it’s a fancy preview mode, with all the nodes folded:

v [{id: 43,…}, {id: 44,…}, {id: 46,…}, {id: 45,…}]
> 0: {id: 43,…}
> 1: {id: 44,…}
> 2: {id: 46,…}
> 3: {id: 45,…}

Not easy to check the shape of the data either.


JSON.stringify to the rescue!

function prettifyJson(json) {
    json,      // copied from Response tab
    undefined, // ignore this argument (or read link below)
    2          // spaces to indent

Paste the above into the Chrome inspector.

Then copy the response in the response tab, and call the function:

>> prettifyJson([{"id":43,"child_node":{"active":true,"name":"name","created_at":"2015-05-25T16:55:09.600-04:00"},"notes":null}])


    "id": 43,
    "child_node": {
      "active": true,
      "name": "name",
      "created_at": "2015-05-25T16:55:09.600-04:00"
    "notes": null

// Tada!!


Written on August 10, 2016 by clemenspark
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RubyMine Highlight for Multi-cursor Drag-and-drop

To create a Multi-cursor in RubyMine with your mouse, hold Alt while dragging your mouse up/down. This is especially useful if you want to adjust tabbing or add some extra characters on consecutive lines.

Written on July 25, 2016 by evanbrodie
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Using WIP acceptance specs


I usually follow the following approaching when working on a story:

  1. Write a failing acceptance spec.
  2. Do a spike to validate the proposed solution. Get the spike to pass.
  3. Capture learnings, and blow away the spike changes.
  4. Properly TDD away at the solution.

One annoyance with this approach was:

What do I do with the failing acceptance spec?

I usually try not to commit failing specs, since that makes git bisect less useful when I’m trying to see what broke it.


RSpec tags to the rescue.

Configure your specs to ignore wip specs by default:

RSpec.configure do |c|
  c.filter_run_excluding wip: true

Write a WIP spec:

it 'tests my yet-to-be-added feature', :wip do
  "my test"

Run the spec:

rspec my_acceptance_spec.rb --tag=wip

The acceptance spec can be committed, because it won’t run as part of your regular test suite.

Once the story is done, make sure you remove the :wip flag!

Written on July 15, 2016 by clemenspark
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Rails assignment operation implicitly updates DB

In Rails, you may fall into a trap where simply assigning a value to an ActiveRecord object’s properties may cause a DB write immediately.

This will occur implicitly without!

What’s vulnerable? It appears that ActiveRecord objects that expose a property via association are vulnerable to this quirk. This won’t happen for properties that have no association.

For example, given the following:

class MyClass < ActiveRecord::Base

has_many :children

attr_accessor :property_name



obj = MyClass.find(1)

obj.children = [child_one, child_two, child_three] <=== this will write to the DB immediately!

obj.property_name = 'value' <=== this is in memory only, the DB has not been updated <=== property_name is updated in the DB now

This may cause issues if your save implies validations and the validations fail. In this case, the associated property was updated in the DB but the other properties were not because of the validation failure.


Written on July 5, 2016 by jordanneville
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[GIT] Change capitalization of file


For example, let’s say that you had a file called myfile.js and you wanted to rename it to MyFile.js. This change would not be recognized in git status and therefore cannot be committed because none of the characters actually changed. It appears that git treats files in a ignores-case way when scanning for changes. Whereas, if I added or removed any of the characters in that name, ie MyFile1.js, then git would recognize the rename.


As per this Stackoverflow post, you can still commit this filename capitalization change using a git mv command. So in this example, we would want to execute this:

git mv myfile.js MyFile.js
Written on June 30, 2016 by evanbrodie
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RubyMine group search by Test and Production code

When I do code searches in RubyMine, I sometimes want to only see non-test code for various reasons, such as knowing how often a particular method is used in our code base to judge adoption level. Normally, I would have to select each directory and run a code search one at a time, or search all directories at once and carefully skip over all test code while scrolling through the list. In a Rails app, directories that contain non-test source code could include app/, domain/, lib/ and even more.

There is a better way! The RubyMine Search tab has a toggle that will let you group source code search by Production and Test code. All you have to do is press this toggle and voila!

Written on June 7, 2016 by evanbrodie
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A little thing about .to_str

Playing with Ruby’s === today and found some knowledge that’s share-worthy. I noticed in ruby docs for “string ===” a reference to “.to_str” and decided to investigate.

Nothing too exciting here, but its an important point of reference.

> hello = "hello"
> goodbye = "goodbye"
> hello === hello     #=> true
> hello === goodbye   #=> false

This is also what would usually be expected. Hang in there…

> string = "string"
> object =
> string + object     #=> TypeError no implicit conversion

Here’s where things get funky.

class SomeObjectWithToStr
  def to_str
    "is now a string"

> string = "string"
> object =

> string + object     #=> "string is now a string"
> "string is now a string" === "string" + object      #=> true

Hunh? Why did that work?

TIL that .to_str is the default method call when operators force a conversion to a string. You’ll likely have to define it yourself. Also note that the object type on the left is what the object type on the right will try to convert into.

Do you know of any Objects that come with pre-defined .to_str methods?

Written on June 1, 2016 by ryanmagowan
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Temporarily skip an RSpec example group

I knew about prefixing an RSpec example with x to skip it. I just found out that a describe or context example group can also be temporarily skipped using xdescribe and xcontext.

How did I find out? RTSL

Special bonus: the focus effect works similarly: fit, fdescribe, and fcontext.

Written on June 1, 2016 by alistairmckinnell
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Usage of $0 in the Chrome dev tools

In the Chrome dev console, typing $0 evaluates to the last selected HTML element (by clicking on it under the ‘Elements’ tab). $1 is the second last selected, up to $4 - and despite the $ this works independently of jQuery.

Written on May 30, 2016 by fabricecastel
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validates_presence_of won't work with booleans

If you want to validate that a value for a particular boolean field exists (using ActiveRecord instead of null constraints from you DB), then you cannot use validates_presence_of. This is due to the way that the blank? works on an object with the value false. Instead, you will need to use this for your validation:

 validates_inclusion_of :field_name, :in => [true, false]


Written on May 24, 2016 by evanbrodie
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Database Column "type" is reserved in Rails

I made a database column called “type”. It contained a string. It was bound to Object. Everything was cool.

I wanted to create my object. But I kept getting this error.

object = Object.create(food: "P&L Burger", name: "The Matty", type: "Burgers")

Invalid single-table inheritance type: 1 is not a subclass of Object

TIL that Rails has some reserved keywords for database column names. It just so happens that the column name “type” is reserved. There are also other reserved column names.

See: Active Record Basics: 2.2 Schema Conventions

The “type” column is reserved for single-table-inheritance where the Ruby Object name would be stored in the “type” column and would be accessible through object.type #=> Object

See: Single Table Inheritance

Written on May 20, 2016 by ryanmagowan
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Learning lessons the hard way: git clean

I had a huge list of superfluous changes in git that I wanted to clean up. Most of them were additions so doing a git checkout wasn’t going to work.

I followed some instructions online and ran: git clean -r -d -x

The trojan horse of this command is the -x flag which will delete all files in your .gitignore!

This led to a half day of setting up my dev environment again to recover all the lost environmental configurations deleted by this command.

Stay tuned for tomorrow’s lesson: Adventures with rm -rf /

Written on May 17, 2016 by jordanneville
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In RubyMine, shift a line or a whole block of code

RubyMine has a key-mapping for grabbing lines of text in the editor, from cursor focus. If you have your cursor focused anywhere in a line of code you can shift it up or down with the following [default] key bindings:

CMD + SHIFT + Up Arrow || Down Arrow

Supercharge your grabbing
If you want to move an entire block of code without having to highlight the entire block, put your cursor on the definition of the statement and RubyMine will shift the entire block for you.

This can work on blocks defined by module; class; def; if; find more use cases and share because I definitely haven’t uncovered them all yet!

Happy Shifting!

Written on May 12, 2016 by ryanmagowan
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Fix Mac RubyMine Floating Window Bug


On RubyMine in Mac, I want to have my RubyMine IDE in one window but have the Run display in Floating Mode appear in my secondary monitor. The issue, though, is that after I have moved the Run display into my secondary monitor, lose focus to another window, then click back into the Run display, the will suddenly JUMP to the same window as my main RubyMine IDE.


The problem appears to be a conflict with a setting in Mac’s Mission Control. You will need to deselect the “Displays have separate spaces” option in the Mission Control preferences screen, as described here.


Written on May 9, 2016 by evanbrodie
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Enable Mac Keyboard Number Pad in iTerm

If you Mac keyboard’s number pad is not working in iTerm, then follow the steps outlined here:

Looks like the answer is to go into Preferences->Profiles->Keys
and load preset of: xterm with numeric keypad.

You will lose any default key mappings that you already set in your iTerm profile already, so you may want to do this in a brand new profile so you can bring over your old mappings to the new profile and not outright lose them like I just did.

Written on May 4, 2016 by evanbrodie
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Re-run only failed tests through Rspec

In cases where large refactoring is taking place and there are multiple tests across multiple files failing, there’s an easy shortcut built into Rspec that allows you to re-run your specs but only the ones that failed.

The command ——————— rspec –only-failures

This allows for a tighter feedback loop to get failing tests green.

Setup ———- This functionality doesn’t come for free and some simple, but required, setup is necessary. Details about what’s required can be [found here.] (

The quick rundown is your Rspec configuration needs some extra flags set:

RSpec.configure do |c|
  c.example_status_persistence_file_path = "failing_specs.txt" 
  c.run_all_when_everything_filtered = true

This is required so Rspec will output any failing specs to a file and then read from it when --only-failures is specified.

Permanently using this, it’s also a great idea to add it to your .gitignore file.

Written on April 22, 2016 by jordanneville
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Rails console options to make your life better

Often when learning or testing out an implementation in planning, entering into a REPL to get some feedback and play with something more physical is desirable.

Here are some tips to improve your rails console workflow:

Specify the environment you wish to use

Maybe you want to try and reproduce an error in production during your test runs. Maybe you want to seed the database for your development server before having created a seed file. Maybe you’re just feeling wild for the day and want to switch things up.

Rails gives you the option to select the environment for the console session:

>rails c --environment=test [test/development/production/...other...]
>rails c test  # as a shorthand

Note: The default environment is set to development

Sandbox so your DB entries do not persist</h3> Often I find myself wanting to just play around with the current build, knowingly wanting to throw away the changes after. Sandboxing is a great way to do this while reducing your cleanup workflow. ``` >rails c --sandbox >rails c -s ``` This saves you from having to write out the following to return to a seeded state: ``` >rake db:reset RAILS_ENV=[environment] ```

Written on April 20, 2016 by ryanmagowan
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Pinch to zoom in Mac RubyMine


I am presenting some source code during a meeting on RubyMine on my Mac machine. When I plug into the projector, my display resolution becomes quite high, so all text on the projector become very small. Using “CMD +” does not zoom in.


Instead, you will need to pinch the Mac’s touchpad with two fingers to control the zoom. Pinch inwards for zoom-out and outwards for zoom-in. You will need to do this on every code tab you have open.

Thanks for the tip, Sean Kirby.

Written on April 14, 2016 by evanbrodie
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What's a "twiddle-wakka"?

I’m proud to say that I now know what a “twiddle-wakka” is. It is the notation ~> that we use in our Ruby-flavoured semver notation in Gemfile. Specifically, it means that the accepted version must be at the same level of the specified version. All sub-levels below the next increment of the current level are accepted. For example, ~> 2.0 means 2.0 <= VERSION < 2.1, while ~> 2.0.1 means 2.0.1 <= VERSION < 2.0.2.


But seriously, now I know what a “twiddle-wakka” is. :D

Written on April 14, 2016 by evanbrodie
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Get Overwritten/Discarded Commits using reflog

git reflog

shows commits including the overwritten/discarded ones. This is useful in case of accidents such as unwanted git commit --amend and git reset.




git reflog --date=iso

to include dates.

Written on April 14, 2016 by joneriksuero
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Rails 4 Strong Parameters Gotcha: Array in Params

When using strong parameters in Rails 4, any non-scalar parameters must be permitted using a special syntax. The following example is for when you are passing in an array of scalar values in a request parameter (and you are using Rails 4 Strong Parameters to whitelist the parameter).

Firstly, note that the following will not work (i.e. the spec will fail):

# routes.rb
post '/thing/create' => 'thing#create'

# thing_controller_spec.rb
RSpec.describe ThingController, type: :controller do
  example do
    post :create, things: [1, 2, 3]

    expect(response.body).to eq('1,2,3')

# thing_controller.rb
class ThingController < ApplicationController
  def create
    permitted_params = params.permit(:things)
    render inline: permitted_params[:things].join(',')

Why does it fail? Rails is expecting a scalar value to be passed in the :things parameter. However, we pass in an array, so Rails silently removes the parameter, even though it is included in the call to params.permit.

In order to make the spec pass, we update the implementation as follows:

# thing_controller.rb
class ThingController < ApplicationController
  def create
    permitted_params = params.permit(things: [])
    render inline: permitted_params[:things].join(',')

For more info about strong parameters, especially in regards to how to permit non-scalar and nested parameters, please refer to:

Written on April 12, 2016 by paulsobocinski
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Enhancing rake tasks


I have a rake task, and I want to make it do something before and after it’s done.

task :a_task do
  puts "task"

task :setup_task do
  puts "setup"

task :run_after do
  puts "after"

What are my options?


For pre-req tasks, this is what is often done:

task :a_task => [:setup_task] do
  puts "task"

task :setup_task do
  puts "setup"
> rake a_task

However, this requires modifying the existing task. This might not even be an option for rake tasks from 3rd party gems. We can do better: Enhance the task!

task :a_task do
  puts "task"

task :setup_task do
  puts "setup"

Rake::Task[:a_task].enhance [:setup_task]
> rake a_task

To run a task (or any code for that matter) after a rake task:

task :a_task do
  puts "task"

task :run_after do
  puts "after"

Rake::Task["a_task"].enhance do
> rake a_task


Written on April 11, 2016 by clemenspark
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Expect to Receive and Call to Original

In integration specs, it is preferable to call the original method when setting up an expectation on an object to receive an invocation of that method. This way, the method isn’t stubbed out but instead will still be invoked. Any downstream effects of calling that method won’t be hidden.

class Calculator
  def self.add(x, y)
    x + y

Should be tested like this:

require 'calculator'

RSpec.describe "and_call_original" do
  it "responds as it normally would" do
    expect(Calculator).to receive(:add).and_call_original
    expect(Calculator.add(2, 3)).to eq(5)  # any bugs inside of #add won't be hidden

This code example is taken from: Relish - Calling the original implementation

Written on April 8, 2016 by shahriyarnasir
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Share a TTY under Linux


  1. Set the screen binary (/usr/bin/screen) setuid root. By default, screen is installed with the setuid bit turned off, as this is a potential security hole.

  2. The teacher starts screen in a local xterm, for example via screen -S SessionName. The -S switch gives the session a name, which makes multiple screen sessions easier to manage.

  3. The student uses SSH to connect to the teacher’s computer.

  4. The teacher then has to allow multiuser access in the screen session via the command Ctrl-a :multiuser on (all screen commands start with the screen escape sequence, Ctrl-a).

  5. Next the teacher grants permission to the student user to access the screen session with Ctrl-a :acladd student where student is the student login ID.

The student can now connect to the teacher’s screen session. The syntax to connect to another user’s screen session is screen -x username/session.

Written on April 7, 2016 by ianpenney
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Unicode Entry on Mac OSX

If you have the code point of a Unicode character, it is possible to enter these characters into (almost) any program on Mac OSX, by first jumping through a few hoops:

  • Open Language & Region.
  • At the bottom right, open Keyboard Preferences…
  • Click the plus sign at the bottom left to add a new Input Source.
  • Under the Others category, select the Unicode Hex Input source.
  • Check the Show Input menu in menu bar option.

You should now see a country flag in your menu bar, which will allow you to switch between different Input Sources (e.g. Canadian English, U.S, Unicode Hex Input). Whenever you want to enter Unicode characters, switch to the Unicode Hex Input source.

Now, you can hold down ⌥ (Option/Alt) and enter your code point to type Unicode characters. For instance, the ⌥ character has code point 2325 and can be entered by holding Option and entering “2325”.

Written on April 6, 2016 by ryandevilla
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Disabling emdash substitutions in OSX apps


I use the slack app on my Mac, but it keeps replacing double dashes with an emdash.

e.g. –stat becomes —stat


In the slack app (and many other apps I presume?), right-click the field that has the problem, and turn off this option:

Substitutions -> Smart Dashes
Written on April 6, 2016 by clemenspark
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Diffing a topic branch against the base branch

I often want to check all the changes made in my branch, relative to the base branch. Let’s say the base branch is master.

Most of the time, I use plain ol’ git diff.

git diff master
git diff master --name-only  # only list the changed files

However, git diff master doesn’t always work. For example, if I pulled the latest changes in master, and haven’t rebased my branch, then git diff master will show all kinds of changes I didn’t make.

So what is a dev to do?

git merge-base to the rescue!

Here’s the description from git help merge-base:

Find as good common ancestors as possible for a merge

The following gives me a good commit to compare against:

> git merge-base master HEAD

Therefore, I can check all my changes using:

git diff `git merge-base master HEAD`

zsh function:

gdb() {
  git diff `git merge-base master HEAD` $@
Written on April 5, 2016 by clemenspark
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Git Cherry-Pick A Merge Commit


I picked up work on a topic branch that has a WIP commit. I reset the branch, fix a few lines, then committed. I noticed now that I’m 1 Ahead and 1 Behind on my branch. I should do a force push….but I forgot to! Instead, I pulled and thus created a merge commit. Ruh roh!

             /        \
A --- B --- C --- D --- M --- E --- F

Not only will this merge commit (empty, by the way) make our overall git history look ugly, it is also going to make rebasing off master very difficult, since we will have to resolve a conflict for all future commits (E and F). I want to keep my topic branch flat.


You can escape this mess via a series of git cherry picks. The key part of this is how we applied the cherry-pick on merge commit F. We need to specify which “parent” to base the commit off of.

git checkout -b new_branch
git cherry-pick A
git cherry-pick B
git cherry-pick C
git cherry-pick D
git cherry-pick M -m 1
git cherry-pick E
git cherry-pick F
Written on April 5, 2016 by evanbrodie
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Open a Mingle ticket via Alfred

Open Alfred Preferences -> Features -> Web Search -> Add Custom Search

  • Search URL:{query}
  • Title: Mingle
  • Keyword: mingle

Usage: Open Alfred search, type mingle 9800

Written on April 5, 2016 by seankirby
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iTerm2 Window Arrangements


Over the course of development on a project, there are many common jobs that one may run on a daily basis, such as:

  • Starting a Rails app and watching a log tail
  • Running a Zeus server and monitoring its status
  • Monitoring RSpec output
  • Keeping an IRB session open for quick experiments

I like to have a consistent workspace and layout that I can assume is readily available, as opposed to hunting down multiple terminal windows on my desktop. iTerm2 happens to provide a built-in mechanism for preserving workspaces and layouts.


Once you have all of your iTerm2 panes, windows, and tabs arranged to your liking, you can hit ⌘⇧s (Command-Shift-S) to Save and name your arrangement.

The next time you start iTerm2, you can Restore your saved layout by pressing ⌘⇧r (Command-Shift-R).

Written on April 5, 2016 by ryandevilla
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Show definition of a method at runtime in Ruby

Many people know about method(:foo).source_location to find where a method is defined at runtime. I just found a better way by using pry.

From the pry console, run:

[8] pry(main)> show-source Bar.scoped.where
From: /Users/arturo/.rvm/gems/ruby-2.2.6/gems/activerecord- @ line 132:
Owner: ActiveRecord::QueryMethods
Visibility: public
Number of lines: 7

def where(opts, *rest)
  return self if opts.blank?

  relation = clone
  relation.where_values += build_where(opts, rest)

Happy Hacking!

Written on April 2, 2016 by arturopie
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Quickly find the git commit that broke a test

Git bisect is a very cool tool that automate a binary search for you to find the first “bad” commit. Here is an example on how to find a commit that broke a test:

  1. git bisect start
  2. git bisect good <good_sha> # <good_sha> is any commit where the test is passing
  3. git bisect bad <bad_sha> # <bad_sha> is any commit where the test is failing
  4. git bisect run zeus rspec <broken test> # remove zeus if you don't use it

Git bisect will perform a binary search and run the test on every step. It uses rspec exit status to know if the commit is “good” or “bad” (0 exit status means “good”, otherwise it’s “bad”). When it’s done it will print the first bad commit:

a5cf29ac1dd64e5ce05336f28aa0ffc17e57fc10 is the first bad commit
commit a5cf29ac1dd64e5ce05336f28aa0ffc17e57fc10
Author: Arturo Pie <>
Date:   Fri Apr 1 08:55:31 2016 -0400

    This is the commit message

:040000 040000 b2399ed1361548a743d95aa6aa95e42096f5ffd3 b500421bbfb9bb3dfebee1e45ff2197a7f32a43e M	app
bisect run success

When you are done debugging, run git bisect reset to end the bisect.

Happy Hacking!

Written on April 1, 2016 by arturopie
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Which Javascript Shell?

When it comes to Javascript Shells, there’s a long list to choose from, but typically, when I want to play with Javascript, the easiest way is to simply open up a console in Chrome.

Recently, I’ve switched over to using SpiderMonkey’s Javascript shell because it allows me to execute a JS file and then drop into the shell.


$ brew install spidermonkey

Vanilla Use Case:

Open up a shell with js command:

$ js
js> var obj = {a: 1};
js> obj;

How to execute a file and then drop into the shell:

Given a file example.js with the following contents:

var a = 42;

Execute the file (-f) and continue in interactive mode (-i):

$ js -f example.js -i
js> a;

Check out the docs for a full list of options.

Written on March 30, 2016 by cameronwoloshyn
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Diffing code snippets between large files

Sometimes I like to compare and contrast differences between sections of large files that exhibit textual similarity.

Suppose I want to compare lines 100-200 from FileA.txt with lines 300-400 from FileB.txt. The following can be accomplished from the command line as follows:

diff <(sed -n '100,200p' /path/to/FileA.txt) <(sed -n '300,400p' /path/to/FileB.txt)

You can substitute diff with any program of your choice (try diffuse, meld, or vimdiff).

Written on March 30, 2016 by ryandevilla
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Where Does That git Setting Come From?

Yesterday git config learnt a new --show-origin option to indicate where configuration values come from.

$ git config --show-origin

Note: available in the 2.8.0 release.

Written on March 29, 2016 by alistairmckinnell
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Inheritance does not affect method visibility

Contrary to visibility conventions in other languages such as Java, Ruby methods defined under a private block in a class definition are still accessible by that class’ children:

class Foo

  def private_method!
    p "Hello world!"

class Bar < Foo
  def uses_private_method

b =
b.uses_private_method # => "Hello world!"

This is because the private keyword in Ruby has nothing to do with inheritance; declaring a method as private only adds the restriction that it may not be invoked with an explicit receiver, as illustrated below:

class Quux < Foo
  def explicit_receiver

  def implicit_receiver

q =
q.explicit_receiver # => NoMethodError: private method `private_method!' called for #<Quux:0x007fee689e0ff8>
q.implicit_receiver # => "Hello world!"
Written on March 24, 2016 by ryandevilla
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ActiveRecord #count versus #length

Let’s say you have an ActiveRecord model with a has_many association. Ever wonder why you receive different results from #count and #length after you append to that has_many collection? Consider this rough example where Parent and Kid are ActiveRecords and Parent will has_many :kids:

parent = Parent.create!! name: 'Evan'
puts "Current length is #{}"
puts "Current count is #{}"

The output will be:

Current length is 0
Current count is 1

The difference in results appear to be happening because of how length() and count() compute their results. length() is only considering what is loaded into heap memory (“cached”), while count() will actually check what is loaded into the DB.

Here’s a great blog post about the difference between the two methods, as well as size().

Written on March 24, 2016 by evanbrodie
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Fetch: two approaches for setting a default value

When using #fetch to assign a default value, the default can be passed either as an argument or as a block.

What are the implications for choosing one approach over the other?

# Option 1: block
setting = settings.fetch('key') { default_setting }

#Option 2: argument
setting = settings.fetch('key', default_setting)

When the default value is passed as a block, it is only evaluated when needed (lazy evaluation).

The argument approach could lead to serious performance issues if the default is an expensive operation.

Written on March 24, 2016 by bryanmacdiarmid
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Running past commands from history

There are many ways to search/recall previous commands from the command line but I find the combination of history and !<history_id> to be quite useful, especially when you don’t remember the command you ran. For example:

Show me my previous commands:

> history
  513  git stash pop
  514  rspec spec/some_spec.rb
  517  git diff
  518  git add -p

Re-run the spec command in 514

> !514
Written on March 23, 2016 by jasonyuen
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Mass replace and copy by file extension


I just cloned a Rails project. There are a bunch of files with the .yml.sample extension under the config directory.

I’d like to copy all those files without the .sample prefix.


zsh functions to the rescue!

Add this to your .zshrc file:

autoload -U zmv

Then run:

zmv -C 'config/(*.yml).sample' 'config/$1'

By default, zmv will move files. -C puts it in copy mode.

For more info:

man zshcontrib
Written on March 22, 2016 by clemenspark
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Oh-My-Zsh Plugins List

I feel like I just discovered the Internet when I look at this page:

Written on March 17, 2016 by evanbrodie
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Consider using the #public_send method

Prefer the #public_send method to the #send method.

result_date = date.public_send(operation, delta)

In the example above the first parameter to the #public_send method is either “+” or “-“.

Written on March 17, 2016 by alistairmckinnell
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Stashing untracked files in Git


I have created new files in the process of spiking an implementation, and want to stash them to prevent “Untracked files” from appearing in git status.


Use git stash save -u.

Written on March 15, 2016 by ryandevilla
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How to view changes from only a particular branch

git log master.., assuming your branch was based off of master. If based off of something else, use that branch name (ie, git log production..)

Courtesy of

Written on March 15, 2016 by evanbrodie
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Loading Data into ELK


I want to load data in to Elasticsearch


Modify this script.

require "elasticsearch"
require "typhoeus"
require "typhoeus/adapters/faraday"

client = "localhost:9200")

scope = BackgroundTask
  .where("created_at > '2015-01-01'")
  .where("created_at < '2016-01-01'")

count_so_far = 0

puts "Processing #{scope.count} records"

  .find_in_batches do |tasks|

  puts "#{count_so_far} of #{scope.count}"
  count_so_far += tasks.count

  task_array = do |task|
      create: {
        _index: "background_tasks",
        _type: "task",
        data: {
          task_type: task.type,
          created_at: task.created_at,
          waiting_time: task.queued_at - task.created_at,
          queued_time: task.run_at - task.queued_at,
          processing_time: task.completed_at - task.run_at

  client.bulk(body: task_array)
Written on March 15, 2016 by adamkerr
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Find all commits by a particular author

Do you want to know quickly about all the commits that a single author has pushed? Easy, just run a git log command with the --author` flag, like this:

git log --author=""
Written on March 11, 2016 by evanbrodie
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Problems with Reusing Ruby Standard Class Names

You might want to think twice before making a class that reuses the same name of a Ruby Standard Library class. If undetected, you will get strange hard-to-debug behaviour in your app. Let’s explore further with this Ruby file:

module Utils
  module String
    def self.some_useful_method
      # ...

module Utils
  module Foo
    def self.do_stuff(string)
      raise "Argument '#{string}' is not a string" unless string.is_a?(String)
      # ...

Utils::Foo.do_stuff("Hello World")

Okay, so “Hello World” is a String. And a String is a String, no questions asked. Right? Well…not quite.

RuntimeError: Argument 'Hello World' is not a string

Since Utils::String gets loaded by Ruby, all references to the String constant from code inside the Utils module will resolve to Utils::String. This example may seem simple and obvious, but imagine if these two classes were in separate files, even separate libraries. How would it feel like if you keep getting "string".is_a? String => false in your debugging sessions?

MORAL OF THE STORY: It probably isn’t a good idea to reuse class names from the Ruby Standard Library. Naming the first module to Utils::StringUtils is likely a better idea.

Written on March 11, 2016 by evanbrodie
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Stashing only some of your files

If you want to keep some files and stash the others, use “git add” to add the files you want to keep, and type

git stash --keep-index
Written on March 11, 2016 by hasithapathiraja
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Add a message to git stash


You want to stash a number of patches and add a message to describe what each includes.


Using git stash without arguments stacks your code changes on the top of a the stash stack, and adds a default message: “WIP on branchname …​”. If you stash multiple patches, you may find it difficult to recall what each stash includes:

$ git stash list

stash@{0}: WIP on 1234_add_new_feature: 1a2b3c4 #1234 - updates new feature template
stash@{1}: WIP on 1234_add_new_feature: 1a2b3c4 #1234 - updates new feature template


You can add a message to the the stash by using the save argument:

$ git stash save "refactors how the UI elements are rendered"
$ git stash list

stash@{0}: On 1234_add_new_feature: refactors how the UI elements are rendered
stash@{1}: WIP on 1234_add_new_feature: 1a2b3c4 #1234 - updates new feature template
stash@{2}: WIP on 1234_add_new_feature: 1a2b3c4 #1234 - updates new feature template

This workflow is especially useful when you’re stashing commits while spiking.

Written on March 10, 2016 by cameronwoloshyn
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Capybara !has_content? vs has_no_content?

Let’s say you’re using RSpec and Capybara.

What’s the difference between the following:

  expect(page).to_not have_content("not on page")


  expect(page).to have_no_content("not on page")

Assuming that the content “not on page” is expected to disappear from the page:

The first one will wait until the Capybara default wait time is over (2 seconds), then pass the assertion. The second one will pass as soon as “not on page” disappears from the page.

The reason the first one waits is because has_content? waits for the content to appear. When the timeout expires, it returns false, which passes the to_not assertion.

Never use to_not have_content or !has_content in Capybara.

Written on March 10, 2016 by clemenspark
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Specify Multiple Examples by Line Number to RSpec

I can specify multiple examples as a colon-delimited list of line numbers to RSpec:

ryandv $ rspec my_spec.rb:2:8
Run options: include {:locations=>{"./my_spec.rb"=>[2, 8]}}

Finished in 0.00052 seconds (files took 0.08873 seconds to load)
2 examples, 0 failures
Written on March 10, 2016 by ryandevilla
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Using git stash for spiking

Often, I do a small spike to see if a certain code change makes sense. When it’s time to actually make code changes, I want to start from scratch to do proper TDD. However, sometimes I want to reference the code I spiked out to guide me.

One option is to stash away the spike, and reference it using:

git stash show -v

This will show you the contents of the most recently stashed code.

If it’s not the most recently stashed change, you can specify the stashed change you want to see:

git stash list
git stash show -v @{2}
Written on March 10, 2016 by clemenspark
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RSpec option to quickly fix transient failures


How do I quickly find the smallest set of tests to reproduce a transient RSpec failure?


Sometimes, we find non-deterministic RSpec failures in our test suite that we often call transient failures. These tests only fail when they are run in a specific order (aka, using the same RSpec order seed), and they always pass when run in isolation.


RSpec provides an option to find the minimum number of tests to run to reproduce the failure by doing bisection.

To use it, run RSpec with the order seed of one of the fail runs, and the –bisect option. For example,

rspec spec/cool_feature_spec.rb --seed 21952 --bisect

and RSpec will find the minimum reproduction command.

The minimal reproduction command is:
  rspec './spec/cool_feature_spec.rb[1:1:1,1:1:2]' --seed 21952
Written on March 10, 2016 by arturopie
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Quick switching from a class to spec

RubyMine will attempt to open the relevant spec file for a class you’re working with when you use the keyboard shortcut CMD + SHIFT + T.

Written on March 10, 2016 by bryanmacdiarmid
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Fancy code highlighting in TIL markdown

If you want to have syntax highlighting in your code blocks, put the language you want highlighting for after the opening backticks. This:

some =


some =

Also somewhat works for other languages!

Written on March 10, 2016 by seankirby
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UUID Generation in Ruby Standard Lib

No need for fancy gems in order to generate RFC4122 Version 4 compliant UUID strings.

>> require 'securerandom'
=> true
>> SecureRandom.uuid
=> "af04813c-6d80-4277-b4e7-7193f7413876"
Written on March 10, 2016 by seankirby
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Curly braces vs. do/end: Operation Precedence

Choosing whether you use { ... } or do ... end around your blocks is more than just a stylistic choice in Ruby. It also affects the way that an operation will be executed because your choice also specifies the Operation Precedence to use. In a nutshell, a block curly braces has higher precedence than a block with do/end.

Consider this example from a great Stackoverflow post:

f param { do_something() }

will execute differently than

f param do do_something() end

The former will bind the block to param, while the latter will bind the block to f. The more you know…

Written on March 9, 2016 by evanbrodie
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Jumping/deleting by matching tags

Let’s say you have the following:

def a_method
  "a return value"

If you put your cursor on def and type %, it goes to end.

If you put your cursor on def and type d%, it deletes the entire method!

Written on March 9, 2016 by clemenspark
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Selectively stashing your changes

git stash -p will allow you to interactively stash changes at a patch level (like other git commands that support the -p option)

Written on March 9, 2016 by jasonyuen
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Toggle Do Not Disturb

Option-click the Notification Menu icon to toggle OS X notifications. The icon is most likely in the top right hand corner of your menu bar.

Written on March 9, 2016 by alistairmckinnell
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Removing untracked files/directories in git

To remove untracked files/directories, use git-clean.

Running git-clean prints out what it would remove, without actually removing them.

-f flag removes the files and -d flag removes empty directories

So to remove untracked files and directories:

git clean -df

To also remove ignored files:

git clean -dfx
Written on March 9, 2016 by hasithapathiraja
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Reverse-search in IRB.

You can reverse-search through previously entered statements in IRB by pressing Ctrl-R:

2.1.6 :001  def something_complicated(x,y); x + y; end
 = :something_complicated
2.1.6 :002  quit

~ 10s
(reverse-i-search)`compli': def something_complicated(x,y); x + y; end

Happy hacking!

Written on March 9, 2016 by ryandevilla
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Search through git commit messages


How do you find the commits associated with a specific story?


At Nulogy, we use a story tracking system that assigns a number to each story. When we’re developing, we tag each commit message with the story number:

$ git commit -m "#1234 - refactors spec"


We can use git log --grep, which greps the commit messages in the repo:

$ git log --grep="#1234"
Written on March 8, 2016 by cameronwoloshyn
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