What are flaky tests and how do you fix them?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of Software Testing & QA conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
A flaky test passes and fails on the same code. Flakiness is corrosive because teams start ignoring failures, which hides real regressions.
Common causes:
- Timing and asynchronous waits: fixed sleeps, race conditions, animations.
- Shared state: tests depending on order, a shared database or global singletons.
- External dependencies: network, third-party APIs, real clocks and random generators.
- Concurrency: parallel test runs colliding on ports, files or data.
- Resource limits: timeouts that fail on slow CI machines.
Fixes:
- Wait for conditions or events, not fixed durations.
- Isolate state, reset the database per test or use transactions and unique data.
- Seed randomness and freeze or inject the clock.
- Quarantine and fix the worst offenders rather than retrying blindly.
- Add retries only as a stopgap and log diagnostics.
Track flake rate over time and treat it as a quality metric, because a suite people trust is worth far more than a large one they ignore.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.