test-coverage.md

Analyze test coverage gaps and generate tests for uncovered code paths.

Steps

1. Run Coverage Analysis

• Detect the test framework and run coverage:
  • JS/TS: npx vitest run --coverage or npx jest --coverage
  • Python: pytest --cov=src --cov-report=term-missing
  • Go: go test -coverprofile=cover.out ./... && go tool cover -func=cover.out
  • Rust: cargo tarpaulin --out Stdout

2. Identify Gaps

• List files below 80% line coverage.
• For each low-coverage file, identify:
  • Uncovered branches (if/else, switch cases, error paths).
  • Uncovered functions or methods.
  • Edge cases not exercised (null inputs, empty collections, boundary values).

3. Prioritize

• Rank gaps by risk: business logic > data access > utilities > configuration.
• Focus on branches where bugs are most likely to hide: error handling, boundary conditions, type coercion.

4. Generate Tests

• Write tests for the highest-priority uncovered paths.
• Each test targets a specific uncovered branch or function.
• Use existing test patterns and conventions from the codebase.
• Follow the Arrange-Act-Assert structure.

5. Verify

• Re-run coverage to confirm the gaps are filled.
• Ensure no existing tests broke.

Rules

• Do not write tests purely to increase numbers. Every test must assert meaningful behavior.
• Exclude generated code, type definitions, and configuration from coverage targets.
• Target 80% line coverage and 75% branch coverage as minimums.
• If a function is genuinely untestable (e.g., thin wrappers), document why rather than writing a meaningless test.