The Bug That Taught Me to Slow Down

A few years into testing, I ran into a bug that only failed about one out of every twenty runs. The test suite flagged it occasionally, someone would re-run the pipeline, it would pass, and everyone would move on. That pattern went on for weeks.

Eventually it stopped being "occasionally" and started showing up in production — a race condition where two requests updating the same record could interleave in just the wrong order, silently overwriting data instead of merging it. It had been failing quietly in CI the entire time. We just hadn't been listening.

The real mistake

The mistake wasn't missing the bug initially — some race conditions are genuinely hard to catch. The mistake was the culture around the flaky test. "It's just flaky, re-run it" had become an automatic reflex, and that reflex trained everyone to stop asking why it was flaky in the first place.

A flaky test is rarely actually random. It's usually a real bug that only reveals itself under specific timing, load, or ordering conditions — which is exactly the kind of bug that's hardest to catch by hand and easiest to catch with the right automated test, if you take the failure seriously instead of re-running past it.

What changed after that

I started treating flaky tests as a signal instead of noise. Any test that failed intermittently got investigated before being re-run, not after. That one habit surfaced two other real race conditions in the following year that would have otherwise shipped.

It also changed how I write tests going forward — deliberately introducing timing pressure, concurrent requests, and out-of-order events into test scenarios instead of only testing the clean, sequential happy path. Most of the bugs that actually hurt users in production live in the gap between "how we expect the system to be used" and "how it's used under real, messy, simultaneous conditions."

Slowing down to actually investigate one annoying, intermittent test failure taught me more about good testing than months of writing straightforward pass/fail checks ever did.