/test-coverage

description: Analyze coverage, identify gaps, and generate missing tests toward the target threshold.

Test Coverage

Analyze test coverage, identify gaps, and generate missing tests to reach 80%+ coverage.

Step 1: Detect Test Framework

| Indicator | Coverage Command | |-----------|-----------------| | `jest.config.*` or `package.json` jest | `npx jest --coverage --coverageReporters=json-summary` | | `vitest.config.*` | `npx vitest run --coverage` | | `pytest.ini` / `pyproject.toml` pytest | `pytest --cov=src --cov-report=json` | | `Cargo.toml` | `cargo llvm-cov --json` | | `pom.xml` with JaCoCo | `mvn test jacoco:report` | | `go.mod` | `go test -coverprofile=coverage.out ./...` |

Step 2: Analyze Coverage Report

1. Run the coverage command 2. Parse the output (JSON summary or terminal output) 3. List files **below 80% coverage**, sorted worst-first 4. For each under-covered file, identify:

• Untested functions or methods
• Missing branch coverage (if/else, switch, error paths)
• Dead code that inflates the denominator

Step 3: Generate Missing Tests

For each under-covered file, generate tests following this priority:

1. **Happy path** — Core functionality with valid inputs 2. **Error handling** — Invalid inputs, missing data, network failures 3. **Edge cases** — Empty arrays, null/undefined, boundary values (0, -1, MAX_INT) 4. **Branch coverage** — Each if/else, switch case, ternary

Test Generation Rules

• Place tests adjacent to source: `foo.ts` → `foo.test.ts` (or project convention)
• Use existing test patterns from the project (import style, assertion library, mocking approach)
• Mock external dependencies (database, APIs, file system)
• Each test should be independent — no shared mutable state between tests
• Name tests descriptively: `test_create_user_with_duplicate_email_returns_409`

Step 4: Verify

1. Run the full test suite — all tests must pass 2. Re-run coverage — verify improvement 3. If still below 80%, repeat Step 3 for remaining gaps

Step 5: Report

Show before/after comparison:

Coverage Report
──────────────────────────────
File                   Before  After
src/services/auth.ts   45%     88%
src/utils/validation.ts 32%    82%
──────────────────────────────
Overall:               67%     84%  PASS:

Focus Areas

• Functions with complex branching (high cyclomatic complexity)
• Error handlers and catch blocks
• Utility functions used across the codebase
• API endpoint handlers (request → response flow)
• Edge cases: null, undefined, empty string, empty array, zero, negative numbers