jest.markdown

Jest

• Setup
  • Using Babel
• Configs
  • Options

Setup

yarn add -D jest babel-jest

package.json

{
    ...
    "scripts": {
    ...
    "test": "jest",
    "test:watch": "npm test -- --watch"
    },
    ...
}

Using Babel

// babel.config.js
module.exports = api => {
  const isTest = api.env("test");

  // You can use isTest to determine what presets and plugins to use.

  return {
    // ...
  };
};

• babel-jest will be installed automatically when installing Jest and will automatically transform files if a babel config exists in your project;
• Jest will set process.env.NODE_ENV to test if it's not already set, you can use that in your babel configuration;

Configs

Config can be defined

• In package.json

  {
      ...
      "jest": {
          "verbose": true,
          ...
      }
      ...
  }

• In jest.config.js

  use jest --init to generate this file

  module.exports = {
    verbose: true
  };

• Using the --config option;

Options

• roots

  Where to find test files and source files, default to ["<rootDir>"]

  {
    "roots": ["<rootDir>/src/", "<rootDir>/tests/"]
  }

• testMatch

  The glob patterns for locating test files, by default it looks for: _ Files in __tests__ folders; _ Files with a suffix of .test or .spec;

  Default:

  {
    "testMatch": [
      "**/__tests__/**/*.[jt]s?(x)",
      "**/?(*.)+(spec|test).[tj]s?(x)"
    ]
  }

• testRegex

  The pattern for locating test files. Use this or testMatch, not both;

• globals

  Can be used in accordance with webpack.DefinePlugin

  {
    "globals": {
      "__DEV__": true
    }
  }

• moduleDirectories

  Use this in accordance with webpack's resolve.modules option

  {
    "moduleDirectories": ["src/components", "node_modules"]
  }

• setupFiles and setupFilesAfterEnv

  • setupFiles files run before each test suite (a .test file), before the testing framework is loaded, could be used to load .env

  • setupFilesAfterEnv files run before each test suite after the testing framework is loaded, so could be used to set options for jest, extending expect, etc

    jest.setTimeout(70000);

  Example:

  setupFiles: ['./jest.setup.js'],
  setupFilesAfterEnv: ['./jest.afterEnvSetup.js'],

  When run jest, the execution order is like:

  running jest.setup.js
  running jest.afterEnvSetup.js
  running a.test.js
  
  running jest.setup.js
  running jest.afterEnvSetup.js
  running b.test.js
  
  ...