alt Hacker NewsI suspect that using a build tag (say `test`) and two function definitions (one that directly calls `time.Now()` and one test-only one that uses a mutable var) will optimize out to zero cost in the non-test case - last I fiddled with that, it was pretty good at consistently inlining trivial wrapper funcs like that.
The compiler will only use _test.go files in the test build - so not an explicit build tag, but a built in one.