Test Coverage

Test Coverage Analysis

Analyze test coverage to identify gaps in critical code paths and produce a prioritized improvement plan.

This skill focuses on analysis only. To write the missing tests, use /write-tests.

Instructions

1. Detect Coverage Tool

   • Auto-detect the project type and identify the appropriate coverage tool:
     • JavaScript/TypeScript: Jest (--coverage), NYC/Istanbul, c8
     • Python: pytest-cov, Coverage.py
     • Java/Kotlin: JaCoCo, Cobertura
     • C#/.NET: dotCover, Coverlet
     • Ruby: SimpleCov
     • Go: go test -cover
     • Rust: cargo-tarpaulin, cargo-llvm-cov
   • Check for existing coverage configuration in project files (jest.config, .coveragerc, jacoco.gradle, etc.)
   • If no coverage tool is configured, recommend one and set it up

2. Run Coverage

   • Execute the test suite with coverage enabled:

     # JavaScript/TypeScript
     npx jest --coverage --coverageReporters=text,lcov
     
     # Python
     pytest --cov=src --cov-report=term --cov-report=html
     
     # Java (Maven)
     mvn clean test jacoco:report
     
     # Go
     go test -coverprofile=coverage.out ./...
     go tool cover -func=coverage.out
     
     # .NET
     dotnet test --collect:"XPlat Code Coverage"
     

   • Capture the output for analysis

3. Analyze Coverage Report

   • Review overall coverage metrics: line, branch, function, and statement coverage
   • Break down coverage by file and directory
   • Identify files with the lowest coverage percentages
   • Pay special attention to branch coverage gaps (untested conditional paths)

4. Identify Critical Gaps

   • Flag uncovered code in business-critical modules (auth, payments, data processing)
   • Identify untested error handling and exception paths
   • Find uncovered public API surfaces and interface methods
   • Note security-sensitive code paths without test coverage
   • Look for untested data validation and input handling

5. Categorize Uncovered Code

   • Must test: Business logic, security controls, data integrity, public APIs
   • Should test: Error handling, edge cases, utility functions
   • Can skip: Auto-generated code, trivial getters/setters, third-party wrappers
   • Consider removing: Dead code with zero coverage and no references

6. Prioritize by Risk

   • Rank gaps by impact: what breaks if this code has a bug?
   • Consider change frequency: files that change often need more coverage
   • Weight by complexity: complex code with many branches is higher risk
   • Factor in user exposure: user-facing code paths are higher priority

7. Produce Improvement Plan

   • Create a prioritized list of files/modules that need coverage improvement
   • For each item, specify:
     • Current coverage percentage
     • Target coverage percentage
     • What types of tests are needed (unit, integration)
     • Estimated effort (small, medium, large)
   • Set realistic overall coverage targets based on project maturity
   • Recommend coverage thresholds for CI/CD gating

8. Configure Coverage Monitoring

   • Recommend or set up coverage reporting in CI/CD
   • Configure coverage threshold enforcement to prevent regression
   • Set up coverage exclusion rules for generated code and vendor files
   • Document exclusion decisions with rationale

To write the missing tests identified in this analysis, use /write-tests.