How do you handle flaky tests?

Flaky test: passes sometimes, fails sometimes; same code, same input. Root cause: hidden non-determinism.

Common causes:

• Time-dependence — Date.today(), DateTime.now() — same input on different days = different results.
• Race conditions — multiple async operations; order varies.
• External dependencies — test depends on network, external service availability.
• Order dependence — tests pass together but fail in isolation (or vice versa).
• Shared state — static variables persist between tests.
• Insufficient waits — UI test acts before page ready.
• Test data drift — SeeAllData=true tests depend on org data.

Detection:

• Run tests 100x in CI; record failure rate.
• Compare passing vs failing logs to find difference.

Root cause analysis:

For each flaky test, ask:

• Time-dependent?
• Async / race condition?
• External dependency?
• Order-dependent?
• Shared state?

Fix patterns:

Time-dependent: Inject TimeService; mock current time.

apex public virtual class TimeService { public virtual DateTime getNow() { return DateTime.now(); } } // Test: provide mock TimeService

Async race: Add Test.startTest() / Test.stopTest() to flush. For UI tests, explicit waits.

External dependency: Mock instead of real call.

Order dependence: Each test sets up own data; no shared state.

Shared state: Reset static variables between tests.

Insufficient waits: Replace Thread.sleep() with explicit conditional waits.

Quarantine:

• If can't fix immediately, mark as flaky.
• Skip in CI but track.
• Don't block releases on flaky tests.

Process:

1. Detect flaky tests.
2. Triage — quarantine if blocking, fix if possible.
3. Root cause systematically.
4. Fix properly.
5. Verify — re-run 100x.
6. Remove from quarantine.

Common pitfalls:

• Ignoring flaky tests — erodes trust in suite.
• Retrying — masks the issue.
• Disabling without quarantine — lost forever.
• No process — flakies accumulate.

Senior QA insight: flaky tests poison the well. They erode developer confidence in the suite. Aggressively address them.

The senior framing: a flaky test is a broken test. Treat with same urgency as a failing test.