Why tests flake more on CI than locally - Code with Jason

A flaky test is a test that passes sometimes and fails sometimes, even though no code has changed.The root cause of flaky tests is some sort of non-determinism, either in the test code or in the application code.In order to understand why a CI test run is more susceptible to flakiness than a local test run, we can go through all the root causes for flakiness one-by-one and consider how a CI test run has a different susceptibility to that specific flaky test cause than a local test run.The root causes we’ll examine (which are all explained in detail in this post) are leaked state, race conditions, network/third-party dependency, fixed time dependency and randomness.