test: use Bun's fake timers to speed up unit tests

[koistya]

Background

Bun v1.3.4 introduced fake timers for bun:test, enabling time manipulation without real delays. This is a great opportunity to speed up our unit tests.

Current state

Our unit tests use manual setTimeout mocking to test timeout behavior. For example, in test/unit/disposable/timeout.test.ts:

const setTimeoutSpy = spyOn(globalThis, "setTimeout")
  .mockImplementation((callback: any, delay: any) => {
    timeoutCallback = callback;
    capturedDelay = delay;
    return 0;
  });

// Later, manually invoke the callback
timeoutCallback();

This works but requires boilerplate and manual callback invocation. Bun's fake timers provide a cleaner API.

Proposal

Refactor unit tests to use Bun's fake timers:

import { jest } from "bun:test";

test("disposal timeout", () => {
  jest.useFakeTimers();
  
  // ... set up test ...
  
  // Advance time instead of manual callback
  jest.advanceTimersByTime(100);
  
  // Assertions...
  
  jest.useRealTimers();
});

Scope

In scope (unit tests only):

• test/unit/disposable/timeout.test.ts — Primary candidate, already mocks setTimeout
• test/unit/disposable/concurrent.test.ts — Uses Bun.sleep() for timing

Out of scope:

• Integration/contract/e2e tests — These test real backend behavior where actual time delays are necessary

Implementation notes

• Bun's fake timers are Jest-compatible: jest.useFakeTimers(), jest.advanceTimersByTime(), jest.useRealTimers()
• Always call useRealTimers() in cleanup to avoid test pollution
• Check Bun docs for full API
• Requires Bun ≥1.3.4 (update @types/bun if needed)

Getting started

1. Read the Bun fake timers docs
2. Start with test/unit/disposable/timeout.test.ts
3. Run bun run test:unit to verify changes
4. Open a PR with the refactored tests

References

• Bun v1.3.4 release notes
• Bun docs: Dates and times
• Jest Timer Mocks (API is compatible)