Restoring Trust in CI: Fixing Flaky Tests at Scale
Platform team (12 engineers) + 6 product squads
6 weeks sprint
E-commerce Marketplace
Tech Stack:
The Problem
CI pipelines were unreliable. 30-40% of test runs failed due to flaky tests (random failures unrelated to code changes). Engineers stopped trusting test results and began merging PRs with failing tests, assuming "it's probably flaky." This eroded quality and allowed real bugs to reach production.
The Approach
We systematically identified, categorized, and eliminated flaky tests using a data-driven approach: (1) instrumented CI to log every test failure with context (browser, environment, timing), (2) analyzed failure patterns to identify top 20 flaky offenders, (3) fixed root causes (race conditions, hardcoded waits, environment dependencies), (4) quarantined unfixable flakes and tracked them separately, (5) established flake rate monitoring to prevent regression.
The Outcomes
- Reduced flaky test failures by 50–75% in 6 weeks
- Improved CI signal reliability: non-product failures dropped by 40–60%
- Increased team confidence in test results from ~30% to 85%+
- Reduced time wasted investigating false failures by 8–12 hours/week per team
- Prevented 15+ real bugs from reaching production in the first month post-fix
What Changed
Before: "Green build" meant nothing because tests were unreliable. Engineers manually re-ran CI 2–3 times hoping for green. After: Teams trusted CI results. Flake rate dropped to < 5%. A red build actually meant something. PRs no longer merged with failing tests.
Services Provided
- •Flaky test identification and root cause analysis
- •CI instrumentation for failure pattern tracking
- •Test infrastructure improvements (timeouts, waits, selectors)
- •Quarantine strategy for unfixable flakes
- •Flake rate monitoring dashboard
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