Test Coverage Analysis Skill

Metadata (Tier 1)

Keywords: coverage, uncovered, pytest-cov, istanbul, c8, coverage report

File Patterns: coverage.xml, lcov.info, coverage.json

Modes: testing_frontend, testing_backend

Instructions (Tier 2)

Python Coverage (coverage.py)

bash

# Generate coverage
pytest --cov=src --cov-report=html --cov-report=term

# Configuration
[tool.coverage.run]
source = ["src"]
branch = true  # Enable branch coverage
omit = ["*/tests/*", "*/__pycache__/*"]

[tool.coverage.report]
fail_under = 80
show_missing = true

JavaScript/TypeScript Coverage

bash

# Jest
npm test -- --coverage

# Vitest
vitest --coverage

# Configuration (vitest.config.ts)
export default defineConfig({
  test: {
    coverage: {
      provider: 'v8',
      reporter: ['text', 'json', 'html'],
      thresholds: {
        lines: 70,
        branches: 70,
        functions: 70,
        statements: 70
      }
    }
  }
});

Coverage Gap Analysis

Critical Gaps (must cover):

•Error handlers (try/except, catch blocks)
•Boundary conditions (null, empty, max values)
•Complex conditionals (nested if/else)
•Security-sensitive code

Example Gap Analysis:

code

File: src/auth.py
Coverage: 45%

Uncovered Lines:
- 45-52: Password reset token generation (CRITICAL)
- 78-85: Email sending error handler (HIGH)
- 120-125: Edge case: empty email (MEDIUM)

Priority: Fix CRITICAL gaps first

Branch Coverage

python

def process(value):
    if value > 0:
        return "positive"  # Branch 1
    else:
        return "non-positive"  # Branch 2

# Need 2 tests to cover both branches
test_process_positive()  # Covers branch 1
test_process_zero()      # Covers branch 2

Coverage in CI/CD

yaml

# GitHub Actions
- name: Test with coverage
  run: pytest --cov=src --cov-report=json

- name: Check threshold
  run: |
    python scripts/coverage_validator.py

Anti-Patterns

❌ Chasing 100% coverage without quality tests ❌ Ignoring branch coverage (only line coverage) ❌ Not testing error paths ❌ Excluding important files from coverage