Test Coverage Analysis & Enhancement

I'll analyze your test coverage, identify untested code paths, and suggest comprehensive tests for uncovered areas.

Arguments: $ARGUMENTS - specific paths or coverage focus areas

Phase 1: Coverage Tool Detection

Pre-Flight Checks: Before starting, I'll verify:

• Test framework and coverage tool availability
• Existing test configuration
• Coverage thresholds and requirements
• CI/CD coverage reporting setup

Coverage Tool Detection:

# Auto-detect coverage tooling
detect_coverage_tool() {
    if [ -f "package.json" ]; then
        # JavaScript/TypeScript ecosystem
        if grep -q "jest" package.json; then
            echo "jest --coverage"
        elif grep -q "vitest" package.json; then
            echo "vitest --coverage"
        elif grep -q "c8" package.json; then
            echo "c8"
        elif grep -q "nyc" package.json || grep -q "istanbul" package.json; then
            echo "nyc"
        fi
    elif [ -f "pyproject.toml" ] || [ -f "setup.py" ]; then
        # Python ecosystem
        if grep -q "pytest-cov" pyproject.toml setup.py requirements.txt 2>/dev/null; then
            echo "pytest-cov"
        elif command -v coverage >/dev/null 2>&1; then
            echo "coverage"
        fi
    elif [ -f "go.mod" ]; then
        # Go has built-in coverage
        echo "go test -cover"
    elif [ -f "Gemfile" ]; then
        # Ruby ecosystem
        if grep -q "simplecov" Gemfile; then
            echo "simplecov"
        fi
    elif [ -f "pom.xml" ] || [ -f "build.gradle" ]; then
        # Java ecosystem
        echo "jacoco"
    fi
}

COVERAGE_TOOL=$(detect_coverage_tool)

if [ -z "$COVERAGE_TOOL" ]; then
    echo "No coverage tool detected. Suggestions:"
    echo "  - JavaScript: npm install --save-dev jest (includes coverage)"
    echo "  - Python: pip install pytest-cov"
    echo "  - Go: Built-in (go test -cover)"
    echo "  - Ruby: gem install simplecov"
    exit 1
fi

echo "Detected coverage tool: $COVERAGE_TOOL"

Coverage Report Generation: I'll use bash to run coverage and parse reports efficiently:

# Generate coverage report with minimal output formats
case "$COVERAGE_TOOL" in
    "jest --coverage")
        # Only generate JSON summary (skip HTML report generation)
        npm test -- --coverage --coverageReporters=json-summary 2>&1 | tail -20
        ;;
    "pytest-cov")
        # Only generate JSON report (skip HTML)
        pytest --cov=. --cov-report=json --cov-report=term-missing:skip-covered 2>&1 | tail -20
        ;;
    "go test -cover")
        go test -coverprofile=coverage.out ./... 2>&1
        go tool cover -func=coverage.out | tail -20
        ;;
esac

# Parse coverage summary (avoid reading thousands of lines of HTML)
if [ -f "coverage/coverage-summary.json" ]; then
    # Jest/NYC format - extract just total metrics
    jq -c '.total' coverage/coverage-summary.json
elif [ -f "coverage.json" ]; then
    # pytest-cov format - extract just summary
    jq -c '.totals' coverage.json
fi

This gets coverage metrics without reading thousands of lines of HTML reports, saving 90%+ tokens.

Phase 2: Coverage Metrics Analysis

I'll analyze multiple coverage dimensions:

1. Line Coverage

   • Percentage of lines executed
   • Identifies completely untested files

2. Branch Coverage

   • Percentage of if/else, switch paths tested
   • More meaningful than line coverage

3. Function Coverage

   • Percentage of functions called
   • Identifies unused code

4. Statement Coverage

   • More granular than line coverage
   • Multiple statements per line counted separately

Coverage Report Parsing:

# Extract low-coverage files for targeted analysis
parse_low_coverage_files() {
    if [ -f "coverage/coverage-summary.json" ]; then
        # Extract files with <80% coverage
        jq -r 'to_entries[] |
               select(.value.lines.pct < 80) |
               "\(.key): \(.value.lines.pct)% lines, \(.value.branches.pct)% branches"' \
               coverage/coverage-summary.json
    fi
}

LOW_COVERAGE_FILES=$(parse_low_coverage_files)

Coverage Threshold Checking:

# Check if project has coverage requirements
check_coverage_thresholds() {
    # Jest configuration
    if [ -f "jest.config.js" ] || [ -f "jest.config.json" ]; then
        grep -A 10 "coverageThreshold" jest.config.* 2>/dev/null
    fi

    # pytest configuration
    if [ -f "pyproject.toml" ]; then
        grep -A 5 "fail_under" pyproject.toml 2>/dev/null
    fi

    # Go coverage threshold (custom)
    if [ -f ".coverage-threshold" ]; then
        cat .coverage-threshold
    fi
}

THRESHOLDS=$(check_coverage_thresholds)

Phase 3: Uncovered Code Identification

Strategic File Analysis:

I'll focus on files with coverage gaps using Grep before full Read:

# Find uncovered functions in low-coverage files (JavaScript/TypeScript)
Grep pattern="^(export )?(async )?function \w+"
     glob="$LOW_COVERAGE_FILE_PATTERN"
     output_mode="content"
     head_limit=15
     -n=true

# Find uncovered classes in low-coverage files (Python)
Grep pattern="^class \w+"
     glob="$LOW_COVERAGE_FILE_PATTERN"
     output_mode="content"
     head_limit=15
     -n=true

# Find error handling that might be uncovered
Grep pattern="throw new|raise |catch \(|except "
     glob="$LOW_COVERAGE_FILE_PATTERN"
     output_mode="content"
     head_limit=10

Uncovered Code Patterns I'll Identify:

1. Error Handling Paths

   try {
       await operation();
   } catch (error) {
       // UNCOVERED: Error path not tested
       logger.error(error);
       throw new CustomError(error);
   }
   

2. Edge Cases in Conditionals

   if (value > 100) {
       return 'high';
   } else if (value > 50) {
       return 'medium';
   } else {
       return 'low'; // UNCOVERED: Never tested
   }
   

3. Validation Logic

   def validate_input(data):
       if not data:
           raise ValueError("Data required")  # UNCOVERED
       if not isinstance(data, dict):
           raise TypeError("Dict required")   # UNCOVERED
       return True
   

4. Async Error Paths

   async function fetchData(url) {
       if (!url) {
           throw new Error('URL required'); // UNCOVERED
       }
   
       const response = await fetch(url);
   
       if (!response.ok) {
           throw new Error('Fetch failed'); // UNCOVERED
       }
   
       return response.json();
   }
   

5. Default/Fallback Cases

   switch (action.type) {
       case 'CREATE':
           return handleCreate(action);
       case 'UPDATE':
           return handleUpdate(action);
       default:
           return state; // UNCOVERED: Default case not tested
   }
   

Phase 4: Missing Test Identification

I'll identify critical gaps:

1. Untested Public APIs

   # Find exported functions
   EXPORTED_FUNCTIONS=$(Grep pattern="^export (async )?function (\w+)"
                             glob="src/**/*.{js,ts}"
                             output_mode="content"
                             head_limit=20)
   
   # Check which ones lack tests (bash comparison)
   echo "$EXPORTED_FUNCTIONS" | while read -r line; do
       FUNC_NAME=$(echo "$line" | grep -oP "function \K\w+")
       # Quick Grep check in test files
       HAS_TEST=$(Grep pattern="$FUNC_NAME"
                       glob="**/*.{test,spec}.*"
                       output_mode="files_with_matches"
                       head_limit=1)
       [ -z "$HAS_TEST" ] && echo "UNTESTED: $FUNC_NAME"
   done
   

2. Untested Error Scenarios

   # Find error throwing code in low-coverage files
   Grep pattern="throw new|raise |throw Error"
        glob="$LOW_COVERAGE_FILE_PATTERN"
        output_mode="content"
        head_limit=15
        -n=true
   

3. Untested Edge Cases

   • Empty array/object handling
   • Null/undefined checks
   • Boundary values (0, -1, MAX_INT)
   • Invalid input types

4. Integration Points

   • API endpoints
   • Database operations
   • External service calls
   • File system operations

Phase 5: Test Suggestions & Generation

For each uncovered area, I'll suggest tests:

Example: Uncovered Error Path

// Uncovered code in src/user-service.js:
async function createUser(data) {
    if (!data.email) {
        throw new Error('Email required'); // UNCOVERED
    }
    return db.users.create(data);
}

// Suggested test:
describe('UserService.createUser', () => {
    it('should throw error when email is missing', async () => {
        await expect(createUser({ name: 'Test' }))
            .rejects.toThrow('Email required');
    });

    it('should throw error when email is null', async () => {
        await expect(createUser({ email: null, name: 'Test' }))
            .rejects.toThrow('Email required');
    });

    it('should throw error when email is empty string', async () => {
        await expect(createUser({ email: '', name: 'Test' }))
            .rejects.toThrow('Email required');
    });
});

Example: Uncovered Branch

# Uncovered code in src/calculator.py:
def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero")  # UNCOVERED
    return a / b

# Suggested test:
def test_divide_by_zero():
    """Test division by zero raises ValueError"""
    with pytest.raises(ValueError, match="Cannot divide by zero"):
        divide(10, 0)

def test_divide_by_negative():
    """Test division by negative number"""
    assert divide(10, -2) == -5.0

def test_divide_floats():
    """Test division with floating point precision"""
    assert abs(divide(1, 3) - 0.333333) < 0.00001

Example: Uncovered Edge Case

// Uncovered code in src/array-utils.js:
function getFirst(arr) {
    return arr[0]; // What if arr is empty? UNCOVERED
}

// Suggested tests:
describe('getFirst', () => {
    it('should return first element of array', () => {
        expect(getFirst([1, 2, 3])).toBe(1);
    });

    it('should return undefined for empty array', () => {
        expect(getFirst([])).toBeUndefined();
    });

    it('should handle single-element array', () => {
        expect(getFirst([42])).toBe(42);
    });

    it('should return first element even if falsy', () => {
        expect(getFirst([0, 1, 2])).toBe(0);
        expect(getFirst([null, 1, 2])).toBeNull();
    });
});

Phase 6: Coverage Improvement Strategy

Prioritization Framework:

I'll prioritize test additions based on:

1. Risk Level (Critical → Low)

   • Critical: Security, data integrity, financial logic
   • High: Core business logic, user-facing features
   • Medium: Utility functions, helpers
   • Low: Logging, formatting, trivial getters

2. Impact (High → Low)

   • High: Code used frequently, critical paths
   • Medium: Occasional use, important features
   • Low: Rarely used, edge features

3. Effort (Low → High)

   • Low: Simple unit tests, pure functions
   • Medium: Mocked integration tests
   • High: Complex integration/E2E tests

Coverage Improvement Plan:

COVERAGE IMPROVEMENT STRATEGY
==============================

Phase 1: Critical Uncovered Code (Priority: High Risk + High Impact)
├── auth/login.js:45-52 - Error handling in authentication
├── payment/process.js:78-85 - Failed payment scenarios
└── user/validate.js:23-30 - Input validation edge cases

Phase 2: Important Features (Priority: High Impact + Low Effort)
├── api/users.js:120-135 - User creation edge cases
├── utils/format.js:45-60 - Edge cases in formatting
└── services/email.js:89-95 - Email send failure handling

Phase 3: Code Quality (Priority: Medium Impact + Low Effort)
├── helpers/string.js:12-25 - String utility edge cases
├── models/user.js:67-72 - Model validation
└── config/parser.js:34-40 - Config parsing errors

Phase 4: Comprehensive Coverage (Priority: Low Risk + Low Effort)
├── utils/constants.js - Getter coverage
├── types/validators.js - Type checking edge cases
└── formatters/date.js - Date formatting edge cases

Phase 7: Test Generation & Implementation

I'll generate and add tests:

1. Create git checkpoint

   git add -A
   git commit -m "Pre test-coverage-improvement checkpoint" || echo "No changes"
   

2. Generate tests for uncovered code:

   • Write comprehensive test cases
   • Cover all branches and edge cases
   • Include descriptive test names
   • Add comments explaining edge cases

3. Verify coverage improvement:

   # Run tests with coverage
   npm test -- --coverage
   
   # Compare before/after coverage
   echo "Coverage improved from X% to Y%"
   

4. Validate test quality:

   • Tests actually assert behavior
   • No false positives (tests that pass without testing)
   • Good test organization and naming
   • Proper setup/teardown

Integration with Existing Skills

Workflow Integration:

• After /test runs → Check coverage with /test-coverage
• After /scaffold → Ensure new code has tests
• Before /commit → Verify coverage thresholds met
• During /review → Include coverage analysis
• With /test-async → Cover async edge cases
• With /test-antipatterns → Quality + coverage together

Skill Suggestions:

• Low coverage in complex async → /test-async
• Coverage but poor quality → /test-antipatterns
• New feature needs tests → /tdd-red-green
• Complex uncovered logic → /explain-like-senior

Reporting

I'll provide comprehensive coverage analysis:

TEST COVERAGE ANALYSIS REPORT
==============================

CURRENT COVERAGE:
├── Lines: 78.5% (target: 80%)
├── Branches: 65.2% (target: 75%)
├── Functions: 82.1% (target: 85%)
└── Statements: 77.8% (target: 80%)

FILES BELOW THRESHOLD:
├── src/auth/login.js: 45.2% (critical!)
├── src/payment/process.js: 52.8% (critical!)
├── src/api/users.js: 71.3%
├── src/utils/validate.js: 68.9%
└── src/helpers/format.js: 74.5%

UNCOVERED CRITICAL CODE:
├── Error handling paths: 23 instances
├── Edge case branches: 18 instances
├── Validation logic: 12 instances
└── Async error paths: 8 instances

TESTS SUGGESTED:
├── Authentication error scenarios: 8 tests
├── Payment failure handling: 6 tests
├── Input validation edge cases: 12 tests
├── API error responses: 10 tests
└── Utility function edge cases: 15 tests

AFTER IMPROVEMENTS:
├── Lines: 78.5% → 87.3% (+8.8%)
├── Branches: 65.2% → 81.7% (+16.5%)
├── Functions: 82.1% → 91.2% (+9.1%)
└── Statements: 77.8% → 86.9% (+9.1%)

TESTS ADDED: 51 new tests
FILES MODIFIED: 12 test files
EXECUTION TIME: +2.3s (acceptable)

NEXT STEPS:
├── Run tests to verify all pass
├── Review generated tests for quality
├── Update CI/CD coverage thresholds
└── Document testing coverage requirements

Coverage Tools Configuration

I can help set up coverage tools:

Jest (JavaScript/TypeScript):

{
  "jest": {
    "collectCoverage": true,
    "coverageDirectory": "coverage",
    "coverageReporters": ["text", "lcov", "json-summary"],
    "coverageThreshold": {
      "global": {
        "lines": 80,
        "branches": 75,
        "functions": 85,
        "statements": 80
      }
    },
    "collectCoverageFrom": [
      "src/**/*.{js,ts}",
      "!src/**/*.d.ts",
      "!src/**/*.test.{js,ts}"
    ]
  }
}

pytest-cov (Python):

[tool.pytest.ini_options]
addopts = "--cov=src --cov-report=term-missing --cov-report=html --cov-fail-under=80"

[tool.coverage.run]
omit = ["*/tests/*", "*/test_*.py"]

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

Safety Guarantees

What I'll NEVER do:

• Generate tests that don't actually test
• Lower coverage thresholds to "pass"
• Test implementation details instead of behavior
• Add AI attribution to commits or code
• Create tests that give false confidence

What I WILL do:

• Generate meaningful, behavior-focused tests
• Cover edge cases and error paths
• Improve actual code quality, not just metrics
• Maintain test maintainability
• Create clear commit messages (no AI attribution)

Credits

This skill is based on:

• Istanbul/nyc - JavaScript coverage tool standards
• Jest - Built-in coverage capabilities
• pytest-cov - Python coverage testing
• JaCoCo - Java code coverage library
• SimpleCov - Ruby coverage analysis
• Testing Best Practices - Community-driven coverage guidelines

Token Optimization

Current Budget: 3,000-5,000 tokens (unoptimized) Optimized Budget: 1,200-2,000 tokens (60% reduction)

This skill implements aggressive token optimization while maintaining comprehensive coverage analysis through strategic tool usage and intelligent reporting.

Optimization Patterns Applied

1. Bash-Based Coverage Tool Execution (90% savings)

# PATTERN: Use direct bash/tool commands, parse JSON, avoid HTML reports
# Savings: 90% vs reading HTML coverage reports

# Generate coverage with minimal output
case "$COVERAGE_TOOL" in
    "jest --coverage")
        # Only JSON summary, skip HTML (saves 4,000+ tokens)
        npm test -- --coverage --silent \
             --coverageReporters=json-summary \
             --no-coverage-reporters=html 2>&1 | tail -20
        ;;
    "pytest-cov")
        # Only JSON, skip HTML and terminal report
        pytest --cov=. --cov-report=json \
               --cov-report=term-missing:skip-covered -q 2>&1 | tail -20
        ;;
esac

# Parse JSON summary directly (50 tokens vs 5,000+ for HTML)
COVERAGE_SUMMARY=$(jq -c '.total' coverage/coverage-summary.json 2>/dev/null)

# Extract just the metrics we need
LINE_PCT=$(echo "$COVERAGE_SUMMARY" | jq -r '.lines.pct')
BRANCH_PCT=$(echo "$COVERAGE_SUMMARY" | jq -r '.branches.pct')
FUNC_PCT=$(echo "$COVERAGE_SUMMARY" | jq -r '.functions.pct')

echo "Coverage: ${LINE_PCT}% lines, ${BRANCH_PCT}% branches"

2. Coverage Tool Detection Caching (saves 500 tokens per run)

# Cache coverage tool detection
CACHE_FILE=".claude/cache/test-coverage/tool.json"

if [ -f "$CACHE_FILE" ]; then
    COVERAGE_TOOL=$(cat "$CACHE_FILE" | jq -r '.tool')
    COVERAGE_COMMAND=$(cat "$CACHE_FILE" | jq -r '.command')
    echo "✓ Using cached coverage tool: $COVERAGE_TOOL"
else
    # Detect tool (first run only)
    if grep -q "jest" package.json 2>/dev/null; then
        COVERAGE_TOOL="jest"
        COVERAGE_COMMAND="npm test -- --coverage --silent --coverageReporters=json-summary"
    elif grep -q "vitest" package.json 2>/dev/null; then
        COVERAGE_TOOL="vitest"
        COVERAGE_COMMAND="vitest --coverage --reporter=json"
    elif grep -q "pytest-cov" pyproject.toml requirements.txt 2>/dev/null; then
        COVERAGE_TOOL="pytest"
        COVERAGE_COMMAND="pytest --cov=. --cov-report=json -q"
    fi

    # Cache result
    mkdir -p .claude/cache/test-coverage
    cat > "$CACHE_FILE" <<EOF
{
  "tool": "$COVERAGE_TOOL",
  "command": "$COVERAGE_COMMAND",
  "timestamp": "$(date -Iseconds)"
}
EOF
fi

3. Early Exit (85% savings when coverage is good)

# PATTERN: Quick validation before deep analysis

# Phase 1: Check if coverage exists (100 tokens)
if [ ! -f "coverage/coverage-summary.json" ] && [ ! -f "coverage.json" ]; then
    echo "Running coverage analysis..."
    $COVERAGE_COMMAND
fi

# Phase 2: Quick coverage check (300 tokens)
LINE_COVERAGE=$(jq -r '.total.lines.pct' coverage/coverage-summary.json 2>/dev/null)
BRANCH_COVERAGE=$(jq -r '.total.branches.pct' coverage/coverage-summary.json 2>/dev/null)

# Check against thresholds
THRESHOLD=${THRESHOLD:-80}

if [ "$(echo "$LINE_COVERAGE >= $THRESHOLD" | bc)" -eq 1 ] && \
   [ "$(echo "$BRANCH_COVERAGE >= 75" | bc)" -eq 1 ]; then
    echo "✓ Coverage meets thresholds:"
    echo "  Lines: ${LINE_COVERAGE}% (target: ${THRESHOLD}%)"
    echo "  Branches: ${BRANCH_COVERAGE}% (target: 75%)"
    exit 0  # Early exit: 400 tokens total (saves 2,500+)
fi

# Phase 3: Deep gap analysis (2,000+ tokens)
# Continue with uncovered code analysis...

4. Progressive Disclosure (75% savings on reporting)

# PATTERN: Tiered reporting based on severity

# Parse verbosity from arguments
VERBOSE=$(echo "$ARGUMENTS" | grep -q "\-\-verbose" && echo "true" || echo "false")
GENERATE=$(echo "$ARGUMENTS" | grep -q "\-\-generate" && echo "true" || echo "false")

# Extract low-coverage files (below threshold)
LOW_COV_FILES=$(jq -r "to_entries[] |
                       select(.value.lines.pct < $THRESHOLD) |
                       \"\(.key): \(.value.lines.pct)%\"" \
                coverage/coverage-summary.json | head -10)

LOW_COUNT=$(echo "$LOW_COV_FILES" | wc -l)

# Level 1 (Default): Critical gaps only
if [ "$VERBOSE" != "true" ]; then
    echo "COVERAGE ANALYSIS:"
    echo "├── Lines: ${LINE_COVERAGE}% (target: ${THRESHOLD}%)"
    echo "├── Branches: ${BRANCH_COVERAGE}% (target: 75%)"
    echo "└── Files below threshold: $LOW_COUNT"
    echo ""
    echo "Critical gaps (top 5):"
    echo "$LOW_COV_FILES" | head -5
    echo ""
    echo "ℹ Run with --verbose to see all gaps"
    echo "ℹ Run with --generate to create tests"
    # Output: ~600 tokens vs 3,000 tokens for full analysis
    exit 0
fi

# Level 2 (--verbose): Detailed gap analysis
if [ "$GENERATE" != "true" ]; then
    echo "DETAILED COVERAGE ANALYSIS:"
    echo ""
    echo "All files below threshold ($LOW_COUNT files):"
    echo "$LOW_COV_FILES"
    echo ""
    echo "Uncovered code patterns:"
    # Show patterns without generating tests
    echo "  - Error handling: X instances"
    echo "  - Edge cases: Y instances"
    echo "  - Validation: Z instances"
    echo ""
    echo "Run with --generate to create suggested tests"
    # Output: ~1,500 tokens
    exit 0
fi

# Level 3 (--verbose --generate): Full test generation
# Generate comprehensive test suggestions (3,000+ tokens)

5. Focus Areas / Scope Limiting (80% savings)

# PATTERN: Default to changed files, allow full coverage analysis

# Parse arguments
FOCUS_PATH="${ARGUMENTS%% *}"
FULL_COVERAGE=$(echo "$ARGUMENTS" | grep -q "\-\-full" && echo "true" || echo "false")
CRITICAL_ONLY=$(echo "$ARGUMENTS" | grep -q "\-\-critical" && echo "true" || echo "false")

if [ "$FULL_COVERAGE" != "true" ]; then
    if [ -n "$FOCUS_PATH" ] && [ -d "$FOCUS_PATH" ]; then
        # Specific path provided
        echo "🔍 Coverage analysis for: $FOCUS_PATH"
        COVERAGE_FILTER="$FOCUS_PATH"
    else
        # Default: Git diff (changed files only)
        CHANGED_FILES=$(git diff --name-only HEAD | \
                       grep -v "\.test\." | \
                       grep -E "\.(js|ts|py|go)$" || echo "")

        if [ -n "$CHANGED_FILES" ]; then
            FILE_COUNT=$(echo "$CHANGED_FILES" | wc -l)
            echo "🔍 Coverage analysis for changed files only ($FILE_COUNT files)"
            echo "  Use --full flag for complete coverage analysis"

            # Filter coverage report to changed files only
            LOW_COV_FILES=$(echo "$LOW_COV_FILES" | \
                           grep -F "$(echo "$CHANGED_FILES" | tr '\n' '|')")

            if [ -z "$LOW_COV_FILES" ]; then
                echo "✓ All changed files have adequate coverage"
                exit 0  # Early exit: no work needed
            fi
        else
            echo "✓ No changed source files detected"
            exit 0
        fi
    fi
else
    echo "🔍 Full project coverage analysis"
fi

# Critical path filtering
if [ "$CRITICAL_ONLY" = "true" ]; then
    echo "  Filtering for critical paths only (auth, payment, security)"
    LOW_COV_FILES=$(echo "$LOW_COV_FILES" | \
                   grep -E "auth|payment|security|login|billing")
fi

# Token savings:
# - Changed files only: ~1,000 tokens (5-10 files)
# - Critical paths only: ~800 tokens (focused analysis)
# - Specific path: ~1,200 tokens (directory focus)
# - Full coverage: ~5,000 tokens (entire project)
# Average savings: 80% (most users analyze changes only)

6. Low-Coverage File Filtering (85% savings)

# PATTERN: Only analyze files below coverage threshold

# Extract files with coverage < threshold from JSON
LOW_COV_FILES=$(jq -r "to_entries[] |
                       select(.value.lines.pct < $THRESHOLD) |
                       .key" \
                coverage/coverage-summary.json)

LOW_COV_COUNT=$(echo "$LOW_COV_FILES" | wc -l)

if [ "$LOW_COV_COUNT" -eq 0 ]; then
    echo "✓ All files meet coverage threshold (${THRESHOLD}%)"
    exit 0  # Early exit: no files to analyze
fi

# Only read files that need attention
echo "Analyzing $LOW_COV_COUNT low-coverage files..."

# Convert to glob pattern for Grep
LOW_COV_PATTERN=$(echo "$LOW_COV_FILES" | head -10 | \
                 sed 's/^/{/' | sed 's/$/,/' | tr '\n' ' ' | \
                 sed 's/,$/}/')

# Now use Grep only on low-coverage files
Grep pattern="throw new|raise "
     glob="$LOW_COV_PATTERN"
     output_mode="content"
     head_limit=15

# Savings: 85% by skipping well-covered files

7. JSON Parsing (95% savings vs HTML)

# PATTERN: Parse JSON coverage reports, never read HTML

# Bad: Read HTML coverage report (5,000+ tokens)
# Read coverage/index.html
# Parse with complex regex...

# Good: Parse JSON summary (200 tokens)
COVERAGE_DATA=$(cat coverage/coverage-summary.json)

# Extract exactly what we need with jq
TOTAL_COVERAGE=$(echo "$COVERAGE_DATA" | jq -c '.total')
LOW_FILES=$(echo "$COVERAGE_DATA" | \
           jq -r "to_entries[] |
                  select(.value.lines.pct < 80) |
                  \"\(.key): \(.value.lines.pct)%\"")

# Just the metrics, no HTML parsing overhead
# Savings: 95% (200 tokens vs 5,000+)

8. Grep-Before-Read for Uncovered Patterns (90% savings)

# PATTERN: Use Grep to find uncovered code patterns in low-coverage files

# Only search in files with low coverage (already filtered)
# Find error handling (likely uncovered)
ERROR_PATTERNS=$(Grep pattern="throw new|raise |catch \(|except "
                      glob="$LOW_COV_PATTERN"
                      output_mode="content"
                      head_limit=10
                      -n=true)

# Find validation logic (often uncovered)
VALIDATION_PATTERNS=$(Grep pattern="if \(!|if \w+ === null|if \w+ === undefined"
                           glob="$LOW_COV_PATTERN"
                           output_mode="content"
                           head_limit=10)

# Find edge case branches (commonly missed)
EDGE_CASES=$(Grep pattern="else if|elif |default:|otherwise"
                  glob="$LOW_COV_PATTERN"
                  output_mode="content"
                  head_limit=10)

# Only read files if we need detailed context for test generation
# Most of the time, patterns are enough for suggestions
# Savings: 90% by avoiding full file reads

Token Budget Breakdown

Optimized Execution Flow:

Phase 1: Coverage Metrics Check (400 tokens)
├─ Tool detection from cache (50 tokens)
├─ Run coverage tool (100 tokens)
├─ Parse JSON summary (100 tokens)
└─ Check against thresholds (150 tokens)
   → Total: 400 tokens (75% of runs exit here - coverage is good)

Phase 2: Low-Coverage File Identification (800 tokens)
├─ Extract files below threshold (200 tokens)
├─ Filter to changed files (200 tokens)
├─ Critical path filtering (100 tokens)
└─ Report top gaps (300 tokens)
   → Total: 1,200 tokens (15% of runs exit here)

Phase 3: Deep Gap Analysis (1,800 tokens)
├─ Grep for uncovered patterns (600 tokens)
├─ Suggest tests (800 tokens)
└─ Generate improvement plan (400 tokens)
   → Total: 3,000 tokens (10% of runs need deep analysis)

Phase 4: Test Generation (only with --generate)
├─ Read low-coverage files (1,000 tokens)
├─ Generate comprehensive tests (1,500 tokens)
└─ Validate and report (500 tokens)
   → Total: 6,000 tokens (rare, only when explicitly requested)

Average: (0.75 × 400) + (0.15 × 1,200) + (0.10 × 3,000) = 780 tokens
Worst case (no --generate): 3,000 tokens
Full generation: 6,000 tokens (explicit opt-in)

Comparison:

Scenario	Unoptimized	Optimized	Savings
Coverage above threshold	4,000	400	90%
Changed files, minor gaps	4,500	1,200	73%
Critical path focus	5,000	800	84%
Deep gap analysis	5,000	3,000	40%
Full test generation	8,000	6,000	25%
Average	5,000	2,000	60%

Cache Strategy

Cache Location: .claude/cache/test-coverage/

Cached Data:

{
  "tool": "jest|vitest|pytest-cov|go-test|simplecov",
  "command": "npm test -- --coverage --coverageReporters=json-summary",
  "thresholds": {
    "lines": 80,
    "branches": 75,
    "functions": 85,
    "statements": 80
  },
  "timestamp": "2026-01-27T10:30:00Z",
  "last_coverage": {
    "lines": 78.5,
    "branches": 65.2,
    "functions": 82.1,
    "statements": 77.8,
    "low_coverage_files": 12,
    "file_checksums": {
      "src/auth.js": "abc123...",
      "src/payment.js": "def456..."
    }
  }
}

Cache Invalidation:

• Time-based: 30 minutes for coverage tool detection
• Source file changes: Re-run coverage if files modified
• Manual: --no-cache flag to force fresh coverage run

Cache Benefits:

• Tool detection: 500 token savings (99% cache hit rate)
• Previous coverage: 2,000 token savings (when source unchanged)
• Overall: 70% savings on repeated runs

Real-World Token Usage

Scenario 1: Daily TDD workflow (most common)

# Developer adds tests, runs /test-coverage

Result:
- Tool: cached (50 tokens)
- Run coverage (100 tokens)
- Coverage: 85% lines, 78% branches (100 tokens)
- Check thresholds: PASS (100 tokens)
- Early exit with ✓ message (50 tokens)
Total: ~400 tokens (92% savings vs 5,000 unoptimized)

Scenario 2: Pre-commit check with gaps

# Developer checks coverage before committing

Result:
- Tool: cached (50 tokens)
- Coverage: 76% lines (below 80% threshold) (100 tokens)
- Changed files: 3 files analyzed (500 tokens)
- Found 2 uncovered error paths (300 tokens)
- Test suggestions for 2 gaps (400 tokens)
Total: ~1,350 tokens (73% savings vs 5,000 unoptimized)

Scenario 3: Critical path audit

# Team lead checks critical auth/payment coverage

Result:
- Tool: cached (50 tokens)
- Full coverage run (200 tokens)
- Filter: --critical flag (100 tokens)
- Found 3 critical files with gaps (400 tokens)
- Detailed uncovered patterns (500 tokens)
Total: ~1,250 tokens (75% savings vs 5,000 unoptimized)

Scenario 4: New feature comprehensive coverage

# Developer wants full test generation

Result:
- Tool: cached (50 tokens)
- Coverage for new feature path (300 tokens)
- Deep pattern analysis (800 tokens)
- Generate tests: --generate flag (2,500 tokens)
- 12 new tests created (1,000 tokens)
Total: ~4,650 tokens (7% savings but complete test suite)

Performance Improvements

Benefits of Optimization:

1. Instant Feedback: 400 tokens when coverage is good (most common)
2. Lower Costs: 60% average token reduction = 60% cost savings
3. Focused Analysis: Only analyze files that need attention
4. Scalability: JSON parsing works on any project size
5. Smart Defaults: Changed files only, expandable to full project

Quality Maintained:

• ✅ Zero functionality regression
• ✅ All coverage metrics still reported
• ✅ Uncovered code patterns still detected
• ✅ Test suggestions remain comprehensive
• ✅ Progressive disclosure improves UX

Additional Optimizations:

• Shared cache with /test and /test-antipatterns skills
• Incremental coverage (only re-run for changed files)
• Parallel test generation (multiple files at once)
• Smart threshold detection from project config

This ensures thorough coverage analysis and meaningful test generation while delivering fast, cost-effective results with actionable insights.