Jest

https://jestjs.io/docs/getting-started
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Jest is a delightful JavaScript Testing Framework designed for simplicity and ease of use. It...
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### Install Babel Preset for TypeScript (npm)

Source: https://jestjs.io/docs/getting-started/index

Installs the Babel preset for TypeScript support for Jest. This is a development dependency.

```bash
npm install --save-dev @babel/preset-typescript  
```

--------------------------------

### Install ts-jest for TypeScript (npm)

Source: https://jestjs.io/docs/getting-started/index

Installs ts-jest, a TypeScript preprocessor with source map support for Jest, as a development dependency.

```bash
npm install --save-dev ts-jest  
```

--------------------------------

### Install Babel Preset for TypeScript (pnpm)

Source: https://jestjs.io/docs/getting-started/index

Installs the Babel preset for TypeScript support for Jest using pnpm. This is a development dependency.

```bash
pnpm add --save-dev @babel/preset-typescript  
```

--------------------------------

### Install Jest with npm, Yarn, or pnpm

Source: https://jestjs.io/docs/getting-started/index

Install Jest as a development dependency using your preferred package manager. This command adds Jest to your project's devDependencies.

```bash
npm install --save-dev jest  
```

```bash
yarn add --dev jest  
```

```bash
pnpm add --save-dev jest  
```

--------------------------------

### Install Babel Preset for TypeScript (Yarn)

Source: https://jestjs.io/docs/getting-started/index

Installs the Babel preset for TypeScript support for Jest using Yarn. This is a development dependency.

```bash
yarn add --dev @babel/preset-typescript  
```

--------------------------------

### Install ts-jest for TypeScript (pnpm)

Source: https://jestjs.io/docs/getting-started/index

Installs ts-jest using pnpm, a TypeScript preprocessor with source map support for Jest, as a development dependency.

```bash
pnpm add --save-dev ts-jest  
```

--------------------------------

### Install ts-jest for TypeScript (Yarn)

Source: https://jestjs.io/docs/getting-started/index

Installs ts-jest using Yarn, a TypeScript preprocessor with source map support for Jest, as a development dependency.

```bash
yarn add --dev ts-jest  
```

--------------------------------

### Run Jest tests from the command line

Source: https://jestjs.io/docs/getting-started/index

Execute Jest tests directly from the command line with various options. This example shows how to run tests matching 'my-test', use a configuration file, and enable notifications.

```bash
jest my-test --notify --config=config.json  
```

--------------------------------

### Install @types/jest for Jest Globals (npm)

Source: https://jestjs.io/docs/getting-started/index

Installs the @types/jest package using npm, which provides types for Jest globals without explicit imports.

```bash
npm install --save-dev @types/jest  
```

--------------------------------

### Install @types/jest for Jest Globals (Yarn)

Source: https://jestjs.io/docs/getting-started/index

Installs the @types/jest package using Yarn, which provides types for Jest globals without explicit imports.

```bash
yarn add --dev @types/jest  
```

--------------------------------

### Install @types/jest for Jest Globals (pnpm)

Source: https://jestjs.io/docs/getting-started/index

Installs the @types/jest package using pnpm, which provides types for Jest globals without explicit imports.

```bash
pnpm add --save-dev @types/jest  
```

--------------------------------

### Install Jest Globals Type Definitions (npm)

Source: https://jestjs.io/docs/getting-started/index

Installs the Jest globals type definitions package for TypeScript projects using npm. This provides type safety for Jest APIs.

```bash
npm install --save-dev @jest/globals  
```

--------------------------------

### Generate a basic Jest configuration file

Source: https://jestjs.io/docs/getting-started/index

Initialize Jest and generate a basic configuration file by running the respective commands for npm, Yarn, or pnpm. Jest will prompt you with questions to customize the configuration.

```bash
npm init jest@latest  
```

```bash
yarn create jest  
```

```bash
pnpm create jest  
```

--------------------------------

### Install Jest Globals Type Definitions (pnpm)

Source: https://jestjs.io/docs/getting-started/index

Installs the Jest globals type definitions package for TypeScript projects using pnpm. This provides type safety for Jest APIs.

```bash
pnpm add --save-dev @jest/globals  
```

--------------------------------

### Install Jest Globals Type Definitions (Yarn)

Source: https://jestjs.io/docs/getting-started/index

Installs the Jest globals type definitions package for TypeScript projects using Yarn. This provides type safety for Jest APIs.

```bash
yarn add --dev @jest/globals  
```

--------------------------------

### Install Babel dependencies for Jest

Source: https://jestjs.io/docs/getting-started/index

Install the necessary Babel packages (`babel-jest`, `@babel/core`, `@babel/preset-env`) as development dependencies using npm, Yarn, or pnpm. These are required for Jest to process modern JavaScript syntax.

```bash
npm install --save-dev babel-jest @babel/core @babel/preset-env  
```

```bash
yarn add --dev babel-jest @babel/core @babel/preset-env  
```

```bash
pnpm add --save-dev babel-jest @babel/core @babel/preset-env  
```

--------------------------------

### Configure Babel for Jest

Source: https://jestjs.io/docs/getting-started/index

Create a `babel.config.js` file to configure Babel for your project, targeting the current Node.js version. This setup ensures Jest can transpile modern JavaScript.

```javascript
module.exports = {  
  presets: [['@babel/preset-env', {targets: {node: 'current'}}]],  
};  
```

--------------------------------

### Configure ESLint with eslint-plugin-jest

Source: https://jestjs.io/docs/getting-started/index

Configures ESLint to enable Jest globals using the 'eslint-plugin-jest'. This is an alternative to configuring globals directly.

```json
{
  "overrides": [
    {
      "files": ["tests/**/*"],
      "plugins": ["jest"],
      "env": {
        "jest/globals": true
      }
    }
  ]
}

```

--------------------------------

### Configure Babel for TypeScript

Source: https://jestjs.io/docs/getting-started/index

Configures Babel to use the preset-env and preset-typescript for Jest. This allows Jest to transpile TypeScript code.

```javascript
module.exports = {
  presets: [
    ['@babel/preset-env', {targets: {node: 'current'}}],
    '@babel/preset-typescript',
  ],
};

```

--------------------------------

### Configure package.json to run Jest tests

Source: https://jestjs.io/docs/getting-started/index

Add a 'test' script to your `package.json` file to easily run Jest tests using `npm test` or `yarn test`. This script executes the Jest command.

```json
{  
  "scripts": {  
    "test": "jest"  
  }  
}  
```

--------------------------------

### Configure ESLint with Jest Globals

Source: https://jestjs.io/docs/getting-started/index

Configures ESLint to recognize Jest globals by extending the 'globals.jest' environment. This avoids 'no-undef' errors.

```javascript
import {defineConfig} from 'eslint/config';
import globals from 'globals';

export default defineConfig([
  {
    files: ['**/*.js'],
    languageOptions: {
      globals: {
        ...globals.jest,
      },
    },
    rules: {
      'no-unused-vars': 'warn',
      'no-undef': 'warn',
    },
  },
]);

```

--------------------------------

### Import Jest APIs in TypeScript Test File

Source: https://jestjs.io/docs/getting-started/index

Demonstrates importing Jest APIs like describe, expect, and test from '@jest/globals' in a TypeScript test file.

```typescript
import {describe, expect, test} from '@jest/globals';
import {sum} from './sum';

describe('sum module', () => {
  test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
  });
});

```

--------------------------------

### Disable Babel transformation in Jest configuration

Source: https://jestjs.io/docs/getting-started/index

If `babel-jest` is automatically transforming files and you want to prevent this, explicitly reset the `transform` option in your `jest.config.js` file to an empty object.

```javascript
module.exports = {  
  transform: {},  
};  
```

--------------------------------

### Conditionally configure Babel for Jest environment

Source: https://jestjs.io/docs/getting-started/index

Use Jest's environment variable (`process.env.NODE_ENV`) within your Babel configuration to conditionally apply transformations. This allows for environment-specific compilation settings.

```javascript
module.exports = api => {  
  const isTest = api.env('test');  
  // You can use isTest to determine what presets and plugins to use.  
  
  return {  
    // ...  
  };  
};  
```

--------------------------------

### Write a basic Jest test for a sum function

Source: https://jestjs.io/docs/getting-started/index

Create a JavaScript file for your function and a corresponding test file using Jest's `test` and `expect` syntax. The test verifies that the `sum` function correctly adds two numbers.

```javascript
function sum(a, b) {  
  return a + b;  
}  
module.exports = sum;  
```

```javascript
const sum = require('./sum');  
  
test('adds 1 + 2 to equal 3', () => {  
  expect(sum(1, 2)).toBe(3);  
});  
```
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