🐢 The Cost of a Slow Test Suite
Slow feedback loops kill velocity more than missing coverage. Here's the math on why speed matters more than you think.
Do the Math
Let's say your test suite takes 10 minutes to run. Seems reasonable, right?
Now multiply:
- 10 minutes × 50 developers × 5 runs per day = 2,500 minutes lost daily
That's 41 hours. Every day. Just waiting for tests.
The Behavioral Cost
The math is bad, but the behavioral changes are worse.
When a suite takes 10+ minutes, developers stop running it locally. They push code, open a PR, and context-switch to something else while CI churns away.
When tests finally fail, they've already forgotten what they were working on. Debugging takes twice as long because they have to reload the mental context.
Eventually, they start making "small" commits without running tests at all. "It's just a one-liner, what could go wrong?"
Everything goes wrong.
The Critical Path
You don't need to make every test fast. You need to make the critical path fast.
That means:
- Tests developers run before pushing (smoke tests, unit tests)
- Tests that gate PR merges (integration tests)
If your full E2E suite takes 30 minutes, fine—run it nightly. But the feedback loop for active development should be under 5 minutes, ideally under 2.
One Priority
Measure time-to-feedback from commit to test results. Track it weekly. If it's trending up, treat it like a production incident.
A test suite that nobody runs is just expensive documentation.