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This repo contains examples of testing react application with react-testing-library and enzyme. It serves as a reference point and a sandbox to experiment with different use cases.

Overview

Revisiting react testing in 2019

Testing React applications is complicated and there are lot of opinions on how it should be done. Examples in this repo are heavily influenced by JavaScript / React testing evangelist: Kent Dodds. The gist of his ideas can be summarized through a number of quotes.

Write tests. Not too many. Mostly integration.

The more your tests resemble the way your software is used, the more confidence they can give you.

The reason this kind of test fails those considerations is because it’s testing irrelevant implementation details. The user does not care one bit what things are called. Why I Never Use Shallow Rendering.

— Kent Dodds

Refactoring an enzyme component test to use react testing library is a side by side comparison of two test frameworks.

Discussion in unlock project

Unit level examples

Repo also includes a number of unit level examples that illustrate pieces required to put together complete integration tests.

  • Mocking fetch post and get methods
  • Waiting for Async methods
  • Chai assertions
  • Chai as promised
  • Testing react router

End to end integration tests for Comments component

  • Rendering assertions
  • Navigation assertions
  • Form validation and submitting
  • Working Redux store
  • Mocking of get and post calls to remote service

Original article that is the source of Comments List example

Enzyme vs React testing library compare with HiddenMessage tests

This code illustrates discussion in Why I Never Use Shallow Rendering.

Frameworks used

Jest

Javascript testing framework, provides engine to execute tests. https://jestjs.io/docs/en/getting-started

Do not manually install jest with: npm install --save-dev jest. Foundation of react projects react-scripts has its own jest dependency.

Chai

Assertion library (can be used with any testing framework) https://www.chaijs.com/

Chai as Promised

Extends Chai with a fluent language for asserting facts about promises. https://www.chaijs.com/plugins/chai-as-promised/

npm install —save-dev chai chai-as-promised

Eslint chai friendly

Chai shortcut syntax expect(...).to.be.null triggers default eslint validation This plugin overrides it for just chai expressions. https://www.npmjs.com/package/eslint-plugin-chai-friendly

npm install eslint-plugin-chai-friendly

React Testing Library

Builds on top of DOM Testing Library by adding APIs for working with React components. https://testing-library.com/docs/react-testing-library/intro

npm install --save-dev @testing-library/react

Latest version suggests react-dom of 16.9, that triggers warnings around component lifecycle methods in form components.

Fetch mock

fetch-mock allows mocking http requests made using fetch or a library imitating its api, such as node-fetch or isomorphic-fetch. http://www.wheresrhys.co.uk/fetch-mock/

Enzyme

JavaScript Testing utility for React that makes it easier to test your React Components' output. You can also manipulate, traverse, and in some ways simulate runtime given the output. Enzyme's API is meant to be intuitive and flexible by mimicking jQuery's API for DOM manipulation and traversal.

https://airbnb.io/enzyme/

Enzyme cheat sheet

Available Scripts

This project was bootstrapped with Create React App.

It also uses

In the project directory, you can run:

npm start

Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

npm test

Launches the test runner in the interactive watch mode.
See the section about running tests for more information.

npm test -- --coverage

Will report test coverage for the project.

Interesting patterns and Gotchas

  1. Forms require working redux store with reducers or fields will not react to changes.

  2. isomorphic-fetch must be imported as follows or mock will not work

    import 'isomorphic-fetch';

  3. Make sure that browser router does not interfere with in memory router or initial values will not work

    const rrd = require('react-router-dom');
rrd.BrowserRouter = ({children}) => <div>{children}</div>;
module.exports = rrd;

  4. Shortcut to map dispatch to props

  5. await waitForElement(() => getByText("O"));

TODO

Open questions

  1. Preferred framework?

  2. Keep the other framework in the projects for special cases or remove completely to avoid accidental use?

  3. Test location?

    • same directory as component under test or
    • __tests__ directory

  4. What tests are expected as part of done?

  5. Next steps?

    • Update on-boarding docs;