Slides, notes and sample project from a talk on testing React applications given at the London React meetup group
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docs Update talk draft notes Mar 24, 2015

React Testability

This is a simple Twitter client project which demonstrates various tools and techniques for writing tests for React components, written as part of a talk (slides, video) at the London React meetup.

It shows the essentials for writing tests for a React application that can be run in Node and the browser, isolating modules under test using shallow rendering and rewire() and using Flummox for testable use of the Flux architecture.


  • NodeJS 4.x or later is required in order to use the current version of the jsdom library.

Building and running

npm install .

# run the app
# (you can also use 'webpack-dev-server')
python -m SimpleHTTPServer 8000
open http://localhost:8000

# run tests in the browser
open tests.html

# run tests on the command-line
make test

Libraries and Tools Used

  • React (obviously). v0.13 is used for shallow-rendering support which enables testing of rendering of a single level of the component tree in isolation. Update (28/02/16): Shallow rendering support has since improved in React v0.14.7 to include some support for stateful components
  • Mocha and chai are the basic testing frameworks used, these were chosen as they are popular, polished and well documented.
  • Webpack is used to package the tests for running/debugging in the browser.
  • jsdom is used for testing of rendering DOM components outside of the browser.
  • The Flummox implementation of the Flux architecture is used for fetching data and updating views in response. Flummox avoidance of singletons makes it easy to inject fake/mock actions in unit and integration tests. Update (28/02/16): Flummox still works perfectly well, but Redux has since become the de-facto choice for state management in the React community and it has an even better testability story.
  • Rewire is used to show one approach to mocking out React components in tests. Update (28/02/16): I would probably recommend looking at inject-loader for Webpack or Proxyquire for Browserify instead as these provide a cleaner way to mock JS modules in my view.
  • isomorphic-fetch provides a uniform API for fetching data in the browser and Node.

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