How to Find and Fix Flaky Tests in Jest The most common root causes of Jest flakiness — and battle-tested fixes you can apply today. March 28, 2026 · 14 min read Jest is the most popular JavaScript testing framework, powering test suites at companies from startups to Fortune 500s. It’s also one of the most common sources of flaky tests. The combination of parallel test execution, module mocking, and shared Node.js process state creates a perfect storm for intermittent failures. If your CI pipeline randomly fails with tests that pass on re-run, this guide is for you. We’ll cover why Jest tests become flaky, how to identify the culprits, and concrete fixes for each pattern — with code you can copy into your codebase today. Want to skip the guesswork? Before you start debugging one test at a time, get a ranked list of your flakiest tests. Kleore scans your CI history and shows you exactly which Jest tests are flaky, how often they fail, and how much each one costs in wasted CI minutes and developer time.…