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Testing Lab 1: Your First Component Test

Objectives​

  • Install React Testing Library
  • Create Your First Component Test

Steps​

This lab is designed to start with the code after finishing:

Lab 25: Redux with React

info

In these testing labs, Create React App was used to create the React application. Create React App is no longer actively maintained but it is an easy way to create a React application that is already setup to do testing with Jest and React Testing Library. The rest of this course has been updated to use the maintained and modern Vite project to create your react application but I continue to include this section because their are millions of applications that are still being maintained that were created using Create React App and use Jest as the JavaScript testing library.

Install React Testing Library​

  1. Make a new directory in your code directory testing.

  2. In that directory, download or clone the following branch to start testing.

    git clone https://github.com/craigmckeachie/keeptrack-js.git keeptrack
    cd keeptrack
    git checkout lab25

    OR

    Visit this link and click Code > Download

  3. Open a command prompt (Windows) or terminal (Mac).

  4. Change the current directory to code\testing\keeptrack.

  5. Run one of the following commands to install the project dependencies:

    npm​

    npm install

    Yarn​

    yarn install

  6. Run one of the following commands to run the tests:

    npm​

    npm test

    Yarn​

    yarn test

  7. Press a to run all tests.

  8. Verify the test created by Create React App fails.

    FAIL  src/App.test.js
    Unable to find an element with the text: /learn react/i.

  9. Open the keeptrack directory in the editor of your choice and then open the file src/App.test.js

  10. Update the test code.

    import React from 'react';
    import { render } from '@testing-library/react';
    import App from './App';

    - test('renders learn react link', () => {
    -  const { getByText } = render(<App />);
    -  const linkElement = getByText(/learn react/i);
    -  expect(linkElement).toBeInTheDocument();
    -});

    + test('should render without crashing', () => {
    + render(<App />);
    + });

    Note: We will test the the content (as the generated test was) in a HomePage component test in the next step.

  11. Verify the test now passes.

    PASS  src/App.test.js

Create Your First Component Test​

  1. Create the file src\home\HomePage.test.js.

  2. Add a test to verify the component shallow renders without crashing.

    src\home\HomePage.test.js​

    import React from 'react';
    import { render, screen } from '@testing-library/react';
    import HomePage from './HomePage';

    test('renders home heading', () => {
      render(<HomePage />);
      expect(screen.getByRole('heading')).toHaveTextContent('Home');
    });

  3. Verify the test passes.

    PASS  src/home/HomePage.test.js

✔ You have completed Testing Lab 1​