Make React PropType warnings throw errors with mocha.js, enzyme.js and sinon.js

react-proptype-warnings-as-errors-with-sinon.markdown

Make React PropType warnings throw errors with enzyme.js + sinon.js + mocha.js

A simple stateless functional component that we want to test that it renders without propType warnings.

import React, { PropTypes } from 'react'

let VersionListItem = function ({ active, version }) {
  return (
    <a href='#' className={`list-group-item ${active}`}>
      <strong
        className='list-group-item-heading'>
        Version {version}
      </strong>
    </a>
  )
}
VersionListItem.propTypes = {
  active: PropTypes.string,
  version: PropTypes.number
}
export default VersionListItem

import { describe, it, before, after } from 'mocha'
import sinon from 'sinon'
import React from 'react'
import { shallow } from 'enzyme'
import VersionListItem from './version-list-item'

// Since react will console.error propType warnings, that which we'd rather have
// as errors, we use sinon.js to stub it into throwing these warning as errors
// instead.
before(() => {
  sinon.stub(console, 'error', (warning) => { throw new Error(warning) })
})
// While not forgetting to restore it afterwards
after(() => { console.error.restore() })

describe('<VersionListItem />', () => {
  const props = {
    active: 'active',
    version: 1
  }

  it('renders without error', () => {
    shallow(<VersionListItem {...props} />)
    // In this case there is no need for an assertion since we're only
    // interested in not getting any errors. And mocha will mark the test as a
    // failure if an error is thrown. :)
  })
})

Related reading:

• Stack Overflow - How to test React PropTypes through Jest?
• Gist by jsdf - Make React PropType warnings throw errors in Jasmine/Jest

Wow, I had no idea there were comments, forks and lots of stars here. Glad you all found it useful. I barely remember writing this.
@ascoppa good point.
@NaveenThally: Take a look at the sinon documentation http://sinonjs.org/ You might want to use a spy instead. Related reading https://www.sitepoint.com/sinon-tutorial-javascript-testing-mocks-spies-stubs/

I found this to be a bit less polluting:

in my helpers.unit.js:

import sinon from 'sinon';
sinon.stub(console, 'error', (warning) => {
  if (warning && warning.indexOf('Warning: Failed prop type:') > -1) {
    process.nextTick(() => {
      throw new Error(warning);
    });
  }
});

then i run: mocha --require helper.unit.js --compilers babel-register mytest.test.js

@hulkish: Cool.
Protip, see https://mochajs.org/#mochaopts (if you're not already aware of it)

Mocha will attempt to load ./test/mocha.opts as a configuration file of sorts. The lines in this file are combined with any command-line arguments.

@scmx is the console.error.restore() part really necessary? I tried omitting it and there were no issues. I'm not also sure what that part actually does, I tried using it on my Chrome's console and it doesn't recognize restore() as a function. I also looked for it in the documentation but couldn't find any. Am I missing something? Thank you for sharing this!

In my mocha env, this only throws on first run. If I am watching the tests, subsequent runs pass (because prop warnings don't fire.) Has anyone else experienced that?

@janzenz: Sinon stubs console.error to be different and provides the restore function to restore console.error to the original it was before. See http://sinonjs.org/releases/v2.1.0/stubs/

@evandavis: Try changing to beforeEach and afterEach instead of before and after. Perhaps it's being restored too soon.

FWIW (and a bite late to the conversation), but I found this to be helpful in our test setup/helper file

import sinon from 'sinon';

const propTypeWarningMatch = sinon.match((warning) => {
  return typeof(warning) === 'string' &&
    warning.indexOf('Warning: Failed prop type:') > -1;
});

sinon.stub(console, 'error');

console.error.withArgs(propTypeWarningMatch).callsFake((warning) => {
  throw new ReferenceError(warning);
});

console.error.callThrough();

The .callThrough() is necessary to ensure console.error()'s default behavior is used for all warnings that don't match the custom match function.

@hulkish: that snippet doesn't actually fail any of my tests. Removing the process.nextTick fixes it.

Also, we removed the third parameter to #stub in Sinon 2 in favor of #callThrough(). @jgkingston's snippet is the way to go nowadays.

To anyone a bit puzzled reading this in 2019

The process.nextTick will work, but it does not get triggered automatically since you are enqueueing that failure.

It's also important to notice that you shouldn't simply stub all the error messages as that would cause infinite recursion due to errors being thrown inside components which then get caught by boundaries. Boundaries then use using console.error, triggering themselves infinitely.

@jgkingston's approach is more accurate if you want to catch propType warnings only, however, remember to throw in a context which is not the component one.