OBSOLETE ADVICE WARNING

(Update on 2020-04-22): This talk was given a long time ago. Tools and best practices have evolved since then. For more up-to-date information, have a look at:

• The Testing Overview section in the official React docs
• A blog post I wrote about unit-testing React or Preact components

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.

Requirements

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

Building and running

npm install .
make

# 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.

Recommended Reading & Videos

• Awesome React - Testing React Tutorials - Awesome React is a great collection of links for all aspects of building React apps. The section on testing references a number of useful tutorials.
• Separating visual and data-fetching components
• React.js Conf 2015 - Making your app fast with high-performance components. This talk introduces a policy of separating pure visual components from containers which contain data fetching logic.
• Beyond unit testing
• Dave McCabe - Property Testing for React. This is a great talk on how to do property testing, where tests are fed a stream of random but repeatable and plausible inputs, and the testing framework checks that various invariants that you specify hold for all inputs.