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

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}`}>
        Version {version}
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:


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ascoppa commented Aug 20, 2016

If you're only interested on testing PropTypes shouldn't you omit calling shallow and just write <VersionListItem {...props} /> ?

Works for me and keeps the test case simple (with just one concern).


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AleksOrl commented Dec 1, 2016

I use this arcticle as an example for testing components in my project. I have found strange behaviour. I wrote about it on StackOverflow. How to avoid this problem?


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NaveenThally commented Jan 13, 2017

How do i unit test the warnings returned by PropType , i wanted to unit test i.e, on setting a specific value the PropType produces a warning which i wanted to Unit test for the code coverage.


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scmx commented Feb 3, 2017

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 You might want to use a spy instead. Related reading


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hulkish commented Mar 5, 2017

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


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scmx commented Mar 8, 2017

@hulkish: Cool.
Protip, see (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.


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janzenz commented Mar 9, 2017

@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!


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evandavis commented Mar 9, 2017

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?


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scmx commented Mar 28, 2017

@janzenz: Sinon stubs console.error to be different and provides the restore function to restore console.error to the original it was before. See

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


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jgkingston commented Dec 6, 2017

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);


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


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fatso83 commented Mar 14, 2018

@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.

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