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name: Test Coverage description: This skill should be used when the user asks to "analyze test coverage", "find untested code", "check coverage gaps", "improve test coverage", "identify missing tests", "measure code coverage", "test quality analysis", or mentions testing strategies and coverage metrics. version: 1.0.0

Test Coverage Analysis

Comprehensive test coverage analysis skill for measuring coverage, identifying gaps, and improving test quality.

Core Capabilities

Coverage Measurement

Calculate and report code coverage metrics:

Line Coverage:

• Percentage of lines executed by tests
• Target: > 80%
• Critical code paths: > 95%

Branch Coverage:

• Percentage of branches (if/else) tested
• Target: > 70%
• Catches edge cases line coverage misses

Function Coverage:

• Percentage of functions called by tests
• Target: > 90%
• Quick indicator of test breadth

Running coverage:

Copy# Python with pytest-cov
pytest --cov=src --cov-report=html --cov-report=term-missing

# Python with coverage.py
coverage run -m pytest
coverage report -m
coverage html

# JavaScript with Jest
jest --coverage

Gap Identification

Find untested code areas:

Completely Untested Files:

• Files with 0% coverage
• Often forgotten modules
• Priority: New features, critical paths

Partially Tested Functions:

• Functions with some but not all branches tested
• Missing edge cases
• Error handling paths

Untested Code Patterns:

Copy# Show lines not covered
coverage report --show-missing

# List files below threshold
coverage report --fail-under=80

# JSON report for parsing
coverage json -o coverage.json

Test Quality Assessment

Evaluate test effectiveness beyond coverage:

Test-to-Code Ratio:

• Lines of test / Lines of source
• Target: 1:1 to 2:1
• Low ratio may indicate insufficient testing

Assertion Density:

• Assertions per test function
• Target: > 1 per test
• Single assertion per concept (ideally)

Test Independence:

• Tests should not depend on each other
• No shared mutable state
• Proper setup/teardown

Test Clarity:

• Descriptive test names
• Clear arrange/act/assert structure
• Documented test purpose

Coverage Analysis Workflow

Full Coverage Analysis

1. Run test suite: Execute all tests with coverage
2. Generate reports: Create HTML and terminal reports
3. Identify gaps: Find untested files and lines
4. Prioritize: Rank gaps by risk and importance
5. Recommend tests: Suggest specific tests to add

Quick Coverage Check

For rapid assessment:

1. Run coverage on changed files only
2. Compare to baseline coverage
3. Flag regressions
4. Report delta coverage

Coverage Report Format

Summary Report

CopyCoverage Summary
================
Total Coverage: 78.5%
Target: 80.0%
Status: BELOW TARGET

By Component:
┌────────────────┬──────────┬────────┬─────────┐
│ Component      │ Lines    │ Missed │ Coverage│
├────────────────┼──────────┼────────┼─────────┤
│ api/           │ 450      │ 45     │ 90%     │
│ services/      │ 820      │ 180    │ 78%     │
│ repositories/  │ 320      │ 96     │ 70%     │
│ utils/         │ 150      │ 60     │ 60%     │
└────────────────┴──────────┴────────┴─────────┘

Gap Analysis

CopyCritical Gaps (Priority: High)
==============================
1. services/payment.py (45% coverage)
   - process_payment(): Lines 45-78 untested
   - refund_transaction(): Completely untested
   - Error handling: 0% coverage

2. repositories/user_repo.py (62% coverage)
   - delete_user(): Untested
   - bulk_update(): Partial coverage

Test Recommendations

CopyRecommended Tests
=================

1. test_payment_processing.py
   - test_successful_payment()
   - test_payment_insufficient_funds()
   - test_payment_network_error()
   - test_refund_full_amount()
   - test_refund_partial_amount()

2. test_user_repository.py
   - test_delete_user_success()
   - test_delete_user_not_found()
   - test_bulk_update_all_fields()
   - test_bulk_update_partial()

Test Types and Strategies

Unit Tests

Coverage focus:

• Individual functions/methods
• Edge cases and boundaries
• Error conditions

Best practices:

• Fast execution (< 100ms each)
• No external dependencies
• Use mocks/stubs for isolation

Integration Tests

Coverage focus:

• Component interactions
• Database operations
• API endpoints

Best practices:

• Test real integrations
• Use test databases/containers
• Clean up after tests

End-to-End Tests

Coverage focus:

• User workflows
• Critical paths
• System behavior

Best practices:

• Selective coverage (key flows)
• Realistic test data
• Stable test environment

Coverage Configuration

Python (pytest-cov)

Copy# pytest.ini or pyproject.toml
[tool.pytest.ini_options]
addopts = "--cov=src --cov-report=term-missing --cov-fail-under=80"

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

[tool.coverage.report]
exclude_lines = [
    "pragma: no cover",
    "if TYPE_CHECKING:",
    "raise NotImplementedError",
]

JavaScript (Jest)

Copy{
  "jest": {
    "collectCoverage": true,
    "coverageThreshold": {
      "global": {
        "branches": 70,
        "functions": 80,
        "lines": 80,
        "statements": 80
      }
    },
    "coveragePathIgnorePatterns": [
      "/node_modules/",
      "/tests/"
    ]
  }
}

Prioritization Framework

Critical (Must Test)

• Payment/financial operations
• Authentication/authorization
• Data validation
• Security-sensitive code
• Core business logic

Important (Should Test)

• User-facing features
• Data transformations
• External integrations
• Error handling paths

Lower Priority

• Utility functions
• Configuration loading
• Logging code
• Debug/development code

Common Coverage Issues

False Sense of Security

Problem: High coverage but weak tests Solution: Review assertion quality, test mutations

Coverage Gaming

Problem: Tests that touch code without verifying behavior Solution: Require meaningful assertions, code review

Untestable Code

Problem: Code that's difficult to test Solution: Refactor for testability, dependency injection

Integration

Coordinate with other skills:

• code-quality skill: For test code quality
• refactoring skill: For improving testability
• security-scanning skill: For security test coverage