Test Coverage
Introduction
Test coverage measures how much of your code is executed during tests. While 100% coverage doesn't guarantee quality, good coverage helps identify untested critical paths.
Coverage Metrics
Understanding Coverage
const COVERAGE_METRICS = {
statements: 'Percentage of statements executed',
branches: 'Percentage of if/else branches tested',
functions: 'Percentage of functions called',
lines: 'Percentage of lines executed',
}
Generating Coverage Reports
Jest Coverage
# Generate coverage report
pnpm test -- --coverage
# View HTML report
open test/coverage/lcov-report/index.html
# Coverage for specific files
pnpm test -- --coverage --collectCoverageFrom="core/lib/**/*.ts"
Coverage Output
-----------------|---------|----------|---------|---------|
File | % Stmts | % Branch | % Funcs | % Lines |
-----------------|---------|----------|---------|---------|
All files | 75.23 | 68.45 | 81.20 | 74.89 |
lib/ | 82.15 | 75.30 | 88.50 | 81.75 |
utils.ts | 90.00 | 85.00 | 95.00 | 89.50 |
validation.ts | 75.00 | 65.00 | 80.00 | 74.00 |
hooks/ | 68.50 | 60.20 | 75.00 | 67.80 |
useDebounce.ts | 85.00 | 80.00 | 90.00 | 84.50 |
-----------------|---------|----------|---------|---------|
Coverage Goals
Target Levels
const COVERAGE_TARGETS = {
critical: {
level: '90%+',
areas: [
'Authentication logic',
'Payment processing',
'Data mutations',
'Permission checks',
]
},
important: {
level: '80%+',
areas: [
'API endpoints',
'Form validation',
'Business logic',
'Entity operations',
]
},
general: {
level: '70%+',
areas: [
'Utilities',
'Helpers',
'Formatting',
'UI components',
]
},
overall: {
target: '75%',
current: '35%',
status: '⚠️ In Progress'
}
}
Improving Coverage
Identify Gaps
# View uncovered lines in report
# Red highlights = not covered
# Green highlights = covered
open test/coverage/lcov-report/index.html
Add Missing Tests
// Found uncovered code:
// utils.ts line 45-50 not covered
// Add test:
describe('utils', () => {
it('should handle edge case from line 45-50', () => {
const result = handleEdgeCase()
expect(result).toBeDefined()
})
})
Coverage in CI/CD
Enforce Minimum Coverage
# .github/workflows/test.yml
- name: Test with coverage
run: pnpm test -- --coverage --coverageThreshold='{"global":{"branches":70,"functions":80,"lines":75,"statements":75}}'
Coverage Badges
# README.md
What NOT to Test
Skip Low-Value Tests
// ❌ Don't test:
// - Third-party libraries
// - Framework code
// - Generated files (registries)
// - Simple getters/setters
// - Type definitions
// ✅ Do test:
// - Business logic
// - Data transformations
// - Validations
// - Edge cases
// - Error handling
Best Practices
✅ DO
// Focus on critical paths first
// 90%+ coverage on auth, payments
// Test behavior, not implementation
// Coverage follows good tests
// Use coverage to find gaps
// Not as a goal itself
// Set realistic targets
// 75% overall is good
❌ DON'T
// Chase 100% coverage blindly
// Diminishing returns after ~80%
// Write tests just for coverage
// Write meaningful tests
// Ignore uncovered critical code
// Low coverage on auth = danger
// Test trivial code
// Focus on what matters
Current Status
Coverage Progress
const CURRENT_COVERAGE = {
date: '2025-11-20',
overall: '35%',
by_area: {
'core/lib/utils': '65%',
'core/lib/db': '45%',
'core/hooks': '40%',
'core/components': '20%',
'app/api': '50%',
},
priority: [
'1. Increase auth coverage to 90%',
'2. Cover all API endpoints (80%)',
'3. Test critical hooks (80%)',
'4. Cover entity operations (75%)',
],
target_date: 'Q1 2025',
target_coverage: '75%',
}
Quick Reference
# Generate coverage
pnpm test -- --coverage
# Watch mode with coverage
pnpm test -- --watch --coverage
# Coverage for changed files only
pnpm test -- --coverage --changedSince=main
# View HTML report
open test/coverage/lcov-report/index.html
Last Updated: 2025-11-20
Version: 1.0.0
Status: In Development
Current Coverage: ~35%
Target: 75%