slow-test-reporter

A comprehensive Jest test reporter that identifies slow tests and provides actionable performance insights to optimize your test suite.

Features

• 📊 Detailed Performance Analysis - Identifies slowest tests with duration statistics
• 📈 Statistical Insights - Provides percentiles, median, standard deviation, and histograms
• 📁 File-level Analysis - Shows which test files consume the most time
• 🏗️ Suite Analysis - Identifies slow test suites and describe blocks
• 💡 Smart Recommendations - Suggests specific optimizations based on your test patterns
• 🎨 Colorized Output - Easy-to-read colored terminal output
• 📋 Multiple Output Formats - Human-readable text or JSON for automation
• ⚡ Overhead Detection - Identifies files with high setup/teardown overhead

Installation

bun:

bun add -d slow-test-reporter

npm:

npm install --save-dev slow-test-reporter

pnpm:

pnpm add -D slow-test-reporter

yarn:

yarn add --dev slow-test-reporter

Usage

Basic Configuration

Add the reporter to your Jest configuration:

// jest.config.js
module.exports = {
  reporters: [
    'default',
    'slow-test-reporter'
  ]
};

With Options

// jest.config.js
module.exports = {
  reporters: [
    'default',
    'slow-test-reporter'
  ]
};

Output Example

Top 30 slowest examples (8.4 s, 18.6% of total time):
  Database migration rollback test
    2.85 s ./src/database/migrations.test.js
  Large file upload with validation
    2.12 s ./src/uploads/fileProcessor.test.js
  Complex authentication flow
    1.94 s ./src/auth/integration.test.js

Average test time: 36.24 ms
Median test time: 18.00 ms
Standard deviation: 127.45 ms
Slowest test is 78.6x slower than average

Percentiles:
  90th: 128.00 ms
  95th: 267.00 ms
  99th: 891.00 ms

Tests exceeding threshold (>300 ms): 15

Duration histogram:
  0-50ms: 1089 ████████████████████████████████████████████████
  51-100ms: 98 ████
  101-200ms: 45 ██
  201-500ms: 12 ▌
  501-1000ms: 2 ▌
  1000ms+: 1 ▌

Top 5 slowest files (by total test duration):
  ./src/database/migrations.test.js: 6.24 s (15 tests, avg: 416.00 ms), overhead: 1.2 s (19.2%)
  ./src/uploads/fileProcessor.test.js: 4.81 s (23 tests, avg: 209.13 ms), overhead: 0.8 s (16.6%)
  ./src/auth/integration.test.js: 3.94 s (8 tests, avg: 492.50 ms), overhead: 0.3 s (7.6%)

Top 5 slowest test suites:
  Database Integration Tests: 8.34 s (28 tests, avg: 297.86 ms)
  File Upload Processing: 6.12 s (31 tests, avg: 197.42 ms)
  Authentication Flows: 4.88 s (19 tests, avg: 256.84 ms)

Recommended Improvements:
- 3 file(s) spend >50% of their runtime in setup/teardown. Potential impact: 2.3 s saved if optimized.
- 2 file(s) are in the top 10% for both test count and total time. Consider splitting/refactoring.
- 5 test(s) are >10x slower than the median. Investigate for unnecessary waits or unmocked dependencies.

## Requirements

- Node.js ≥ 20.0.0
- Jest ≥ 27.0.0

## License

MIT © Doug Schlenker

## Contributing

Issues and pull requests are welcome! Please see the [GitHub repository](https://github.com/schlenks/slow-test-reporter) for more information.