Implementing Test Retries in Jest for Flaky Tests

Flaky tests are a common and frustrating problem in software development. They are tests that sometimes pass and sometimes fail, even when no code has changed. This challenge focuses on implementing a mechanism to automatically retry flaky tests in Jest, improving test suite reliability.

Problem Description

You are tasked with creating a Jest configuration or helper that automatically retries tests that fail. This is particularly useful for tests that interact with external services, have asynchronous operations that can be timing-sensitive, or are otherwise prone to intermittent failures. The goal is to make your test suite more robust by giving flaky tests a second (or third) chance to pass before reporting a failure.

Key Requirements:

• Configure Jest to automatically retry failing tests a specified number of times.
• The retry mechanism should be easily configurable at the test suite level.
• The retried tests should only be executed if they initially fail.
• If a test passes on any retry, it should be marked as passed.
• If a test fails after all retries, it should be marked as failed.

Expected Behavior:

A test that fails once and then passes on the next attempt should be reported as passed. A test that fails multiple times consecutively and exhausts all retry attempts should be reported as failed.

Edge Cases to Consider:

• Tests that consistently fail across all retries.
• Tests that pass on the first attempt (no retries should occur).
• Scenarios where you want to configure retries for specific test files or describe blocks (optional, but good to keep in mind for advanced solutions).

Examples

Example 1:

Let's assume a test that is designed to be flaky, sometimes throwing an error.

Jest Configuration (conceptual): Imagine a jest.config.js or a setup file where we configure retries to 2.

// jest.config.js (conceptual)
module.exports = {
  // ... other Jest configurations
  reporters: [
    "default",
    // Potentially a custom reporter or setup to enable retries
  ],
  // Or a global setup that injects retry logic
  globalSetup: './jest-global-setup.ts',
  testEnvironment: 'node',
};

And a test file:

// my-flaky-test.test.ts

describe('A potentially flaky operation', () => {
  let attemptCount = 0;

  it('should eventually succeed', () => {
    attemptCount++;
    if (attemptCount < 3) { // Simulate flakiness for the first 2 attempts
      throw new Error('Simulated transient error');
    }
    expect(true).toBe(true);
  });
});

Expected Jest Output (with retries = 2):

PASS  my-flaky-test.test.ts
  A potentially flaky operation
    ✓ should eventually succeed (X ms) // Will show as passed after retries

Explanation: The test fails on the first attempt (attemptCount = 1) and the second attempt (attemptCount = 2). Because we configured 2 retries, Jest will run the test again. On the third execution (attemptCount = 3), the test passes, and Jest reports it as a success.

Example 2:

A test that is consistently flaky and fails all retry attempts.

Jest Configuration (conceptual): Same configuration as Example 1, with retries = 2.

Test File:

// another-flaky-test.test.ts

describe('Another flaky operation', () => {
  let attemptCount = 0;

  it('should eventually succeed', () => {
    attemptCount++;
    if (attemptCount < 4) { // Always fails within 3 attempts
      throw new Error('Persistent transient error');
    }
    expect(true).toBe(true);
  });
});

Expected Jest Output (with retries = 2):

FAIL  another-flaky-test.test.ts
  Another flaky operation
    × should eventually succeed (X ms) // Will show as failed after retries

Explanation: The test fails on the first, second, and third executions. With 2 retries, it has a total of 3 attempts. Since it fails all 3 attempts, Jest reports it as a failure.

Constraints

• The retry mechanism should be configurable to a maximum of 5 retries per test.
• The solution must be implemented using TypeScript and Jest.
• The solution should not significantly impact the performance of tests that do not fail initially.
• The solution should ideally integrate with Jest's reporting mechanisms to accurately reflect retry behavior in the output.

Notes

• Jest has a built-in experimental feature for retries (--max-retries CLI flag). However, this challenge encourages you to explore how you might implement this yourself or use existing community solutions that offer more flexibility.
• Consider how you will manage the state of attemptCount for each test.
• Think about how you will integrate your retry logic with Jest's test lifecycle. You might look into Jest's globalSetup, globalTeardown, or custom test reporters.
• For this challenge, focus on implementing the core retry logic. Advanced features like per-test or per-describe block configuration can be considered a bonus.