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shubhambajaj

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Mastering Jest Configuration for React TypeScript Projects with Vite: A Step-by-Step Guide

#jest #vite #react #testing

1. First generate react typescript using vite 

npm create vite@latest
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2. Install dependancies 

npm i jest @types/jest ts-jest --save-dev
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3. Exclude test files from typescript type checking for production

  • Create tsconfig.prod.json and paste following contents into it. 
touch tsconfig.prod.json
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// tsconfig.prod.json
{
  "extends": "./tsconfig",
  "exclude": [
    "./src/__tests__/**",
    "./src/__mocks__/**",
    "./src/test-utils"
  ]
}
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Exclude test files from typescript type checking when building for production, you don’t want a typescript error in your test file breaks your build in production.

—Nguyen Viet Hung, hung.dev
  • Use tsconfig.prod.json when building 
# package.json
{
...,
"scripts":{
  ...,
  "build": "NODE_ENV=production tsc -p tsconfig.prod.json && vite build"
},
...
}
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4. Add test script to package.json 

// package.json
{
...,
"scripts":{
  ...,
  "test": "NODE_ENV=test jest"
},
...
}
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5. Write a simple test 

// src/App.test.tsx

describe('App', () => {
  it('should work as expected', () => {
    expect(1 + 1).toBe(2);
  });
});
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Run the npm run test 🤞, and first test case 😃 passed. 🚀

node 'node_modules/.bin/jest' '/.../code/my-doc-test-app/src/App.test.tsx' -t 'App'
 PASS  src/App.test.tsx
  App
    ✓ should work as expected (1 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.209 s
Ran all test suites matching /...\/code\/my-doc-test-app\/src\/App.test.tsx/i with tests matching "App".
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6. Test the App component 

// src/App.test.tsx
import { render } from '@testing-library/react';
import App from './App';

describe('App', () => {
  it('should work as expected', () => {
    render(<App />);
  });
});
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Run the npm run test 🤞, and test failed. This error will show up.

node 'node_modules/.bin/jest' '/Users/satparkash/code/test-app/src/A
pp.test.tsx' -t 'App'
 FAIL  src/App.test.tsx
  ● Test suite failed to run

    SyntaxError: /Users/satparkash/code/test-app/src/App.test.tsx: Support for the experimental syntax 'jsx' isn't currently enabled (6:12):

      4 | describe('App', () => {
      5 |   it('should work as expected', () => {
    > 6 |     render(<App />);
        |            ^
      7 |   });
      8 | });
      9 |

    Add @babel/preset-react (https://github.com/babel/babel/tree/main/packages/babel-preset-react) to the 'presets' section of your Babel config to enable transformation.
    If you want to leave it as-is, add @babel/plugin-syntax-jsx (https://github.com/babel/babel/tree/main/packages/babel-plugin-syntax-jsx) to the 'plugins' section to enable parsing.

    Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.278 s
Ran all test suites matching /\/Users\/satparkash\/code\/test-app\/src\/App.test.tsx/i with tests matching "App".
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The above ☝️ error message is indicating a syntax related to JSX in test file.
The error is saying that support for the syntax 'JSX' isn't currently enabled.

To resolve the issue we need to make sure that the JSX syntax is properly
configured for project, and also the jest. (Hint: Babel)

7. For JSX support, add babel presets and add .babelrc

  • Firstly Install dependancies 
npm i @babel/preset-env @babel/preset-react @babel/preset-typescript --save-dev
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  • Create .babelrc file at project root, and paste following contents into it. 
touch .babelrc
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//.babelrc
{
  "presets": [
    "@babel/preset-env",
    ["@babel/preset-react", { "runtime": "automatic" }],
    "@babel/preset-typescript"
  ]
}
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8. Install testing library for react

By Now previous error will be gone and you will get new error message.

node 'node_modules/.bin/jest' '/Users/satparkash/code/test-app/src
/App.test.tsx' -t 'App'
 FAIL  src/App.test.tsx
  ● Test suite failed to run

    Cannot find module '@testing-library/react' from 'src/App.test.tsx'

    > 1 | import { render } from '@testing-library/react';
        | ^
      2 | import App from './App';
      3 |
      4 | describe('App', () => {

      at Resolver._throwModNotFoundError (node_modules/jest-resolve/build/resolver.js:427:11)
      at Object.require (src/App.test.tsx:1:1)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.231 s
Ran all test suites matching /\/Users\/satparkash\/code\/test-app\/src\/App.test.tsx/i with tests matching "App"
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Now, you have to add libraries which will allow you to make things happen (access VDOM, interacting …. etc), And those libraries are “@testing-library/dom”, “@testing-library/jest-dom”, “@testing-library/react” and “@testing-library/user-event”

—Mhand 
npm i @testing-library/dom @testing-library/jest-dom @testing-library/react @testing-library/user-event --save-dev
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Now it's time to configure jest-environment. You will see another error message
saying Jest encountered an unexpected token, don't worry we are about to fix
it.

9. Let's Configure Jest

  • Firstly install following dependancies 
npm i ts-node jest-environment-jsdom --save-dev
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  • Create a file jest.config.ts at the root project, and paste following contents into it. 
touch jest.config.ts
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//jest.config.ts
export default {
  rootDir: 'src',
  preset: 'ts-jest',
  testEnvironment: 'jsdom',
  transform: {
    '^.+\\.tsx?$': 'ts-jest',
    // process `*.tsx` files with `ts-jest`
  },
  moduleNameMapper: {
    '\\.(gif|ttf|eot|svg|png)$': '<rootDir>/config/jest/fileMock.ts',
    '^.+\\.(css|less|scss|sass)$': '<rootDir>/config/jest/styleMock.ts',
  },
  setupFilesAfterEnv: ['./config/jest/setupTests.ts'],
  moduleFileExtensions: [
    // Place tsx and ts to beginning as suggestion from Jest team
    // https://jestjs.io/docs/configuration#modulefileextensions-arraystring
    'tsx',
    'ts',
    'web.js',
    'js',
    'web.ts',
    'web.tsx',
    'json',
    'web.jsx',
    'jsx',
    'node',
  ],
  modulePaths: ['<rootDir>/src'],
};
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  • Create config/jest/styleMock.ts, config/jest/fileMock.ts to mock css and files. 
// config/jest/styleMock.ts

module.exports = {};
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// config/jest/fileMock.ts

export {}; //coment this if you ts-node to start complaining again
module.exports = 'test-file-stub';
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  • Create config/jest/setupTests.ts, a file that runs before each test. 
//config/jest/setupTests.ts

// jest-dom adds custom jest matchers for asserting on DOM nodes.
// allows you to do things like:
// expect(element).toHaveTextContent(/react/i)
// learn more: https://github.com/testing-library/jest-dom
import '@testing-library/jest-dom';
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INFO

/**
 *
 * If imported(inside setupTests.ts):
 * import '@testing-library/jest-dom/extend-expect'
 * then we are required to map it inside `jest.config.ts` like this:
 * 

 * // jest.config.ts
 * {
 * ...,
 * moduleNameMapper: {
 * ...,
 *     '@testing-library/jest-dom/extend-expect': '@testing-library/jest-dom',
 * }
 * }
 */
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By this moment, you can run the test successfully😎.

node 'node_modules/.bin/jest' '/Users/satparkash/code/test-app/src/App.test.tsx' -t 'App'
 PASS  src/App.test.tsx
  App
    ✓ should work as expected (12 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.19 s
Ran all test suites matching /\/Users\/satparkash\/code\/test-app\/src\/App.test.tsx/i with tests matching "App".
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Happy testing 😀

10. For Snapsot Testing [optional]

For snapshot testing add react-test-renderer

npm i react-test-renderer --save-dev
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PS: I didnt' implemented snapshot testing 😄 Yet.

11. For import.meta' meta-property is only allowed when the '--module' option is... [error TS1343]

  • Error Message 
error TS1343: The 'import.meta' meta-property is only allowed when the '--module' option is 'es2020', 'es2022', 'esnext', 'system', 'node16', or 'nodenext'.

          .get(import.meta.env.VITE_API_PATH + '/api/posts')
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  • Install dependancy 
npm install -D ts-jest-mock-import-meta
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  • Change the transform to mock import.meta of vite 
// jest.config.ts

export default {

  ...,
    transform: {
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        diagnostics: {
          ignoreCodes: [1343],
        },
        astTransformers: {
          before: [
            {
              path: 'node_modules/ts-jest-mock-import-meta',
              options: {
                metaObjectReplacement: {
                  env: {
                    // Replicate as .env.local
                    VITE_API_PATH: 'http://localhost:3001',
                  },
                },
              },
            },
          ],
        },
      },
    ],
  },
  ...
}
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References

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