I was trying to speed up our slow CI by caching Go builds. The easy win was caching Go’s module downloads (via GOPATH), but when I added GOCACHE for the build cache, I got a pleasant surprise: the tests were caching too. 🥳

I shared the change for review, and a colleague raised a great point: “What about our black box integration tests?” These tests hit APIs and external services that Go can’t track as dependencies. If they cache when they shouldn’t, we might miss real failures: the tests would pass because they didn’t re-run, not because the code actually works.