How to configure Jest? What are the common configuration options?

Jest provides multiple configuration methods to customize test behavior:

1. package.json Configuration:

json
{
  "jest": {
    "testEnvironment": "node",
    "coverageThreshold": {
      "global": {
        "branches": 80,
        "functions": 80,
        "lines": 80,
        "statements": 80
      }
    }
  }
}

2. jest.config.js Configuration File:

javascript
module.exports = {
  testEnvironment: 'jsdom',
  setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1',
    '\\.(css|less|scss)$': 'identity-obj-proxy'
  },
  collectCoverageFrom: [
    'src/**/*.{js,jsx,ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/*.stories.{js,jsx,ts,tsx}'
  ],
  testMatch: [
    '**/__tests__/**/*.{js,jsx,ts,tsx}',
    '**/*.{spec,test}.{js,jsx,ts,tsx}'
  ],
  transform: {
    '^.+\\.(js|jsx|ts|tsx)$': 'babel-jest'
  }
};

Common Configuration Options:

• testEnvironment: Test environment (node, jsdom)
• setupFilesAfterEnv: Test environment setup file
• moduleNameMapper: Module path mapping
• collectCoverageFrom: Coverage collection scope
• testMatch: Test file matching patterns
• transform: File transformation configuration
• coverageThreshold: Coverage thresholds
• testTimeout: Test timeout duration

Command Line Options:

• jest --watch: Watch mode
• jest --coverage: Generate coverage report
• jest --updateSnapshot: Update snapshots
• jest --verbose: Verbose output