Test Asynchronous & Reactive Code

Background: Native [platform] app. The code under test is asynchronous/
reactive: [paste it—e.g., a Combine pipeline, a Flow, an async/await
function, a debounced search]. 

Use case: Write reliable, non-flaky tests for this async behavior.

Implementation details:
- iOS: test async/await directly, or use expectations / a test scheduler
  for Combine; control time for debounce/delay instead of sleeping.
  Android: runTest with the test dispatcher, Turbine (or equivalent) for
  Flow, and virtual time for debounce/delay.
- Never use real wall-clock sleeps—drive virtual time
- Test cancellation, error emission within the stream, and completion
- Assert the sequence of emitted values/states, not just the final one
- Make the tests deterministic so they pass 1000/1000 runs

Deliverable: The async test suite using virtual time / test schedulers,
coverage of emission sequence + error + cancellation, and an explanation
of how flakiness is avoided here.