What Are Flaky Tests? The Silent Killer of CI Pipelines They pass. They fail. Nothing changed. And your team just lost another hour. March 21, 2026 · 8 min read A flaky test is a test that produces different results — pass or fail — when run against the same code. No one touched the source. No dependency changed. Yet the test failed, your build went red, and someone on your team had to stop what they were doing to investigate. Thirty minutes later, they re-run the pipeline. It passes. They shrug, merge the PR, and move on — but the damage is already done: time wasted, context lost, and a little more trust eroded in your test suite. Why do tests become flaky? Flaky tests aren’t random. They have root causes, but those causes are often subtle enough that they don’t surface on every run. The most common culprits: Timing & race conditions Tests that depend on specific timing — setTimeout, polling intervals, animations — fail when the runner is a few milliseconds slower than expected.…