Code Coverage

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Jest Coverage(DOCUMENTATION)

Introduction

Code coverage tells you what percentage of your code is executed during tests. It's a useful metric, but not the only indicator of test quality.

Key Concepts

Coverage types:

  • Statements: % of statements executed
  • Branches: % of if/else branches taken
  • Functions: % of functions called
  • Lines: % of lines executed

Deep Dive

Enabling Coverage

json
// package.json
{
  "scripts": {
    "test:coverage": "jest --coverage"
  }
}

Jest Configuration

javascript
// jest.config.js
module.exports = {
  collectCoverageFrom: [
    'src/**/*.{js,jsx,ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/*.stories.tsx',
  ],
  coverageThreshold: {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80,
    },
  },
};

Interpreting Results

----------------------|---------|----------|---------|---------|-------------------
File                  | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------------------|---------|----------|---------|---------|-------------------
All files             |   85.71 |    83.33 |   88.89 |   85.71 |
components/Button.tsx |     100 |      100 |     100 |     100 |
components/Form.tsx   |   71.43 |    66.67 |   77.78 |   71.43 | 23-27,45
----------------------|---------|----------|---------|---------|-------------------

Summary

Coverage helps identify untested code but doesn't guarantee test quality. Aim for meaningful coverage (80%+) and focus on testing critical paths rather than chasing 100%.

✓ Completed