Reading: Class 36 – Application State Testing with Jest - mwilkin-401-advanced-javascript/bend-javascript-401d2 GitHub Wiki

Testing a React-Redux app using Jest and Enzyme

  • Jest – Unit testing framework for React.js

  • Babel-jest: for support of ES6 and ES7.

  • Enzyme -JS testing utility to make it easier to assert React Components.

Advantages of using Jest for a testing environment:

  • Easy to set up
  • Able to run in parallel with development
  • Fast running testing framework
  • Snapshot testing: reduces the number of tests necessary, able to track changes in the various components
  • Built in matchers, spies, and an extensive mocking library (including manual module mocks, timer mocks, and ES6 class mocks)
  • Jasmine is used for assertion
  • Supports TypeScript
  • Built in Coverage reports
  • Does Delta Testing with watch
  • Very to migrate from other testing solutions

Reducer - a pure function that takes the previous state and an action, and returns the next state.

  • Pure functions are easy to test: they don’t have side-effects, don’t rely on external state and will always return the same output.

    • Usually where the business logic should happen.
    • Where new application state is formed based on external (API) or internal response.

  • Having unit tests for all reducers will prevent any issues related to global application state.

  • Especially useful if there are a lot of different API calls and every call will modify a state.