Today I Learned

Mocha: Fail on any console error message

PROBLEM

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.

SOLUTION

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.