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What causes flaky tests and how do you fix them?

Tags

#flaky#stability#ci

Back to category Practice quiz

Answer

Flaky tests fail nondeterministically due to timing, shared state, or environment issues. Fix them by isolating state, controlling time, waiting for conditions not sleeps, and stabilizing environments.

Advanced answer

Deep dive

Common sources:

Race conditions, async not awaited.
Shared state between tests.
Reliance on external services or clocks.
Order-dependent tests.

Fix strategies:

Use deterministic clocks and random seeds.
Reset state between tests.
Replace sleeps with condition-based waits.
Quarantine flaky tests and track trends.

Examples

Condition-based wait:

waitUntil(() => element.isVisible())

Common pitfalls

Retrying flaky tests without fixing root cause.
Ignoring flakes in CI until they pile up.
Using real network dependencies in unit tests.

Interview follow-ups

How do you detect flaky tests early?
When is retry acceptable?
How do you keep E2E tests stable?

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