| name | go-testing |
| description | Idiomatic Go testing. This skill should be used when the user writes or reviews Go tests, benchmarks, or fuzz targets — table-driven tests, `t.Parallel`, `testing.B.Loop`, the race detector, goroutine-leak detection, `testing/synctest` for time/concurrency, fuzzing, or golden files. Pair with `go test -race`. Not for non-Go test frameworks; error-wrapping belongs to `go-errors`. |
go-testing — Go testing
Deterministic backstop: go test -race ./... (always, in CI), go test -bench, go test -fuzz.
Rules
- Table-driven tests: a named-case slice +
t.Run(tc.name, func(t *testing.T){ … }). Since Go
1.22 the tc := tc copy is unnecessary — drop it (modernize/copyloopvar flag it).
t.Parallel() on independent tests to cut wall-clock; watch for shared mutable state and
loop-var capture in the parallel body.- Benchmarks:
for b.Loop() { … } (Go 1.24) — it handles timer reset and run scaling; replaces
for i := 0; i < b.N; i++ plus manual b.ResetTimer().
-race is non-negotiable for any code touching goroutines; wire it into CI.- Goroutine-leak detection:
go.uber.org/goleak — goleak.VerifyTestMain(m) or per-test
defer goleak.VerifyNone(t).
testing/synctest (stable since Go 1.25) is the default for time/concurrency tests — timeouts,
tickers, retries, context cancellation. It runs the bubble on a fake clock with deterministic
scheduling, so "5-second" waits complete in microseconds and flakiness disappears. Wrap with
synctest.Test(t, func(t *testing.T){ … }); synctest.Wait() blocks until every goroutine in the
bubble is durably blocked. Reach for it instead of time.Sleep-based polling. (The pre-1.25
GOEXPERIMENT=synctest API — synctest.Run — was removed in Go 1.26; use the stable synctest.Test.)- Fuzzing (
func FuzzX(f *testing.F)) for parsers, codecs, and anything consuming untrusted
bytes. Golden files (an -update flag writing testdata/*.golden) for large structured output.
- Deterministic crypto tests (Go 1.26):
testing/cryptotest.SetGlobalRandom(t, seed) pins a
deterministic randomness source for the test's duration — reach for it instead of hand-injecting a
custom io.Reader when testing code that draws from crypto/rand. It's process-global, so it
can't run inside a t.Parallel() test (or one with a parallel ancestor).
- Assertions: stdlib + small helpers (
t.Helper()) is often enough; testify is fine — match
the repo, don't mix styles.
Sources
Decomposition inspired by samber/cc-skills-golang (MIT © 2026 Samuel Berthe); rules grounded in the sources above.
