Managing Jest

Jest Testing Framework Management Skill

Manage and analyze Jest test suites, coverage, and configurations.

Core Helper Functions

#!/bin/bash

# Run Jest with JSON reporter
jest_run() {
    local args="${1:-}"
    npx jest $args --json --outputFile=jest-results.json 2>/dev/null
}

# Parse Jest results
jest_results() {
    cat jest-results.json 2>/dev/null || echo '{"numTotalTests":0,"testResults":[]}'
}

MANDATORY: Discovery-First Pattern

Always discover Jest configuration and test structure before querying specifics.

Phase 1: Discovery

#!/bin/bash

echo "=== Jest Configuration ==="
if [ -f "jest.config.ts" ]; then
    grep -E "(testMatch|testPathIgnorePatterns|coverageThreshold|transform|moduleNameMapper|setupFiles|preset)" jest.config.ts | head -15
elif [ -f "jest.config.js" ]; then
    grep -E "(testMatch|testPathIgnorePatterns|coverageThreshold|transform|moduleNameMapper|setupFiles|preset)" jest.config.js | head -15
else
    node -e "const pkg = require('./package.json'); console.log(JSON.stringify(pkg.jest || {}, null, 2))" 2>/dev/null | head -15
fi

echo ""
echo "=== Jest Version ==="
npx jest --version 2>/dev/null

echo ""
echo "=== Test File Summary ==="
find . -name "*.test.ts" -o -name "*.test.js" -o -name "*.test.tsx" -o -name "*.test.jsx" -o -name "*.spec.ts" -o -name "*.spec.js" 2>/dev/null | grep -v node_modules | wc -l | xargs echo "Total test files:"
find . -name "*.test.ts" -o -name "*.test.tsx" 2>/dev/null | grep -v node_modules | head -15

echo ""
echo "=== Snapshot Files ==="
find . -name "*.snap" 2>/dev/null | grep -v node_modules | wc -l | xargs echo "Snapshot files:"

Phase 2: Analysis

#!/bin/bash

echo "=== Last Test Run Results ==="
if [ -f "jest-results.json" ]; then
    cat jest-results.json | jq '{
        total: .numTotalTests,
        passed: .numPassedTests,
        failed: .numFailedTests,
        pending: .numPendingTests,
        suites_total: .numTotalTestSuites,
        suites_failed: .numFailedTestSuites,
        duration_sec: (.testResults | map(.perfStats.end - .perfStats.start) | add / 1000 | floor)
    }'

    echo ""
    echo "=== Failed Tests ==="
    cat jest-results.json | jq -r '
        .testResults[] | select(.status == "failed") |
        .testResults[] | select(.status == "failed") |
        "\(.ancestorTitles | join(" > ")) > \(.title)\n  \(.failureMessages[0] | split("\n")[0])"
    ' | head -20
fi

echo ""
echo "=== Coverage Summary ==="
if [ -f "coverage/coverage-summary.json" ]; then
    cat coverage/coverage-summary.json | jq '.total | {
        lines: "\(.lines.pct)%",
        branches: "\(.branches.pct)%",
        functions: "\(.functions.pct)%",
        statements: "\(.statements.pct)%"
    }'
fi

Output Rules

• TOKEN EFFICIENCY: Target 50 lines per output
• Parse JSON output rather than console text
• Never dump full snapshots — show only diff summaries

Anti-Hallucination Rules

• NEVER guess test file names — always discover via filesystem
• NEVER fabricate coverage numbers — parse actual coverage-summary.json
• NEVER assume Jest config location — check jest.config.*, package.json

Safety Rules

• NEVER update snapshots without explicit user confirmation
• NEVER modify test files without user approval
• NEVER delete coverage reports without user consent

Output Format

Present results as a structured report:

Managing Jest Report
════════════════════
Resources discovered: [count]

Resource       Status    Key Metric    Issues
──────────────────────────────────────────────
[name]         [ok/warn] [value]       [findings]

Summary: [total] resources | [ok] healthy | [warn] warnings | [crit] critical
Action Items: [list of prioritized findings]

Target ≤50 lines of output. Use tables for multi-resource comparisons.

Counter-Rationalizations