test-coverage-guardian

name	Test Coverage Guardian
description	Analyze test coverage, identify gaps, detect dead code, and improve test quality. Use when user asks to check coverage, review tests, find untested code, or improve test robustness.

Test Coverage Guardian

Analyze and improve test coverage for any codebase.

Configuration

Variable	Default	Description
COVERAGE_CMD	make test-coverage	Command to generate coverage report
COVERAGE_TARGET	80	Target coverage percentage for core modules
TEST_CMD	make test	Command to run tests

Quick Start

Language-specific coverage commands:

# Go
go test -cover ./...
go test -coverprofile=coverage.out ./...
go tool cover -func=coverage.out

# Python
pytest --cov=src --cov-report=term-missing
coverage run -m pytest && coverage report

# JavaScript/TypeScript
npx jest --coverage
npx vitest --coverage

# Rust
cargo tarpaulin --out Html

When to Use This Skill

Invoke when user says:

• "Check test coverage"
• "What's untested?"
• "Review the test suite"
• "Find dead code"
• "Tests keep breaking" (brittleness analysis)

Analysis Workflow

Step 1: Get Current Coverage

Run your project's coverage command and capture the output. Look for overall percentage and per-module/file breakdown.

Step 2: Identify Gaps

# Go: Find 0% coverage functions
go test -coverprofile=coverage.out ./...
go tool cover -func=coverage.out | grep "0.0%"

# Python: Show missing lines
pytest --cov=src --cov-report=term-missing

# JS/TS: Check lcov report
npx jest --coverage --coverageReporters=text

Step 3: Categorize Gaps

Category	Action
Core logic uncovered	Write tests (high priority)
Error paths uncovered	Add error case tests
Dead code (never called)	Consider removal
Experimental code	Accept lower coverage

Step 4: Report Findings

## Coverage Report

### Summary
- Overall: X%
- Core modules: Y%
- Target: ${COVERAGE_TARGET}%+ overall

### Critical Gaps
1. src/types/unifier.ts - type unification (0%)
2. src/eval/effects.py - effect handlers (15%)

### Dead Code Candidates
- src/legacy/old_parser.go (0%, no references)

### Recommendations
1. Add tests for critical gap #1
2. Add integration tests for #2
3. Remove dead code candidates

Coverage Standards

Set targets appropriate to your project:

Module Type	Recommended Target
Core logic / business rules	80%+
API handlers / controllers	70%+
Utilities / helpers	70%+
UI components	60%+
Configuration / setup	50%+

Critical paths (aim for 100%):

• Authentication and authorization
• Data validation and sanitization
• Financial calculations
• Security-sensitive code paths

Test Quality Checklist

Anti-Brittleness

• Tests public APIs, not private implementation
• Uses interface-based testing where appropriate
• Tests error types, not exact messages
• Mocks external dependencies at boundaries
• Tests behavior, not call sequences

Good Patterns

• Table-driven tests for comprehensive inputs
• Property-based tests for invariants
• Error path testing
• Integration tests at module boundaries

CI/CD Monitoring

# View recent CI runs
gh run list --limit 10

# Check failed run
gh run view <run-id> --log-failed

# Watch run in progress
gh run watch <run-id>

Quality Gates

• No PR should decrease overall coverage
• New features must include tests
• Bug fixes must include regression tests
• Breaking changes require test updates

Tips

• Focus on branch coverage, not just line coverage
• Test the sad path - error conditions matter
• Golden tests for complex outputs (parser, codegen)
• Property tests for mathematical invariants