Go testing

Process skills that may load with this one: load-with list.

Iron law

Tests constrain observable behavior, not coverage percentages.

Each case is independently runnable, named, and attributed to its own *testing.T. Coverage is a gap finder. A green percentage with weak assertions is theater.

Always

Ask first

Do not self-except. Record the choice.

Never

Modes (one pass)

Shape

func TestAdd(t *testing.T) {}                 // function
func TestMyStruct_MyMethod(t *testing.T) {}   // method
func BenchmarkAdd(b *testing.B) {}            // benchmark: b.Run per variant; Go 1.24+ b.Loop()
func ExampleAdd() {}                          // example
func FuzzAdd(f *testing.F) {}                 // fuzz

Same-package tests see unexported names. package foo_test sees the public API only. Prefer black-box unless you are testing a package invariant that is not exported.

Split foo_test.go / foo_edgecases_test.go only when one file is genuinely unwieldy — still named from the source file, never from a single function.

Table-driven

func TestCalculatePrice(t *testing.T) {
    tests := []struct {
        name      string
        quantity  int
        unitPrice float64
        want      float64
    }{
        {name: "single item", quantity: 1, unitPrice: 10, want: 10},
        {name: "zero quantity", quantity: 0, unitPrice: 10, want: 0},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := CalculatePrice(tt.quantity, tt.unitPrice)
            if got != tt.want {
                t.Fatalf("CalculatePrice(%d, %.2f) = %.2f, want %.2f",
                    tt.quantity, tt.unitPrice, got, tt.want)
            }
        })
    }
}

stdlib t.Fatalf is enough. If you use testify, build assert.New(t) inside the subtest from that subtest’s t. Probe a broken case: parent FAIL + every --- PASS: Test/case means the assert leaked.

t.Parallel() goes on the subtest (and the parent if the parent has no shared setup). Build the assert after t.Parallel(), from the subtest t.

Integration

//go:build integration

func TestDatabaseIntegration(t *testing.T) { /* real store */ }

go test -tags=integration ./...

Unit tests: fast, no network, no live store. HTTP handlers: net/http/httptest. Go 1.27+ httptest.NewTestServer is the in-memory server that composes with synctest.

Leaks and time

Packages that start goroutines:

func TestMain(m *testing.M) { goleak.VerifyTestMain(m) }

Per-test: defer goleak.VerifyNone(t).

Go 1.25+ testing/synctest: synctest.Test(t, func(t *testing.T) { ... }). Fake time advances when every goroutine in the bubble is blocked — use it for Sleep / After / Ticker / deadlines instead of wall-clock flakes. Go 1.27+ synctest.Sleep(d) advances the bubble clock directly.

Fuzz and examples

Seed with f.Add, then assert an invariant (round-trip, parse/format). ExampleXxx stdout must match // Output:.

Coverage: go test -coverprofile=coverage.out ./... then go tool cover -html=coverage.out. Read uncovered lines. Do not treat the number as DoD.

Linters that catch this skill’s rules: thelper, paralleltest, testifylint. tester owns hook wiring — do not remint CI here.

Commands

go test ./...                     # unit (no integration tag)
go test -race ./...               # CI default for concurrent packages
go test -run TestName/case ./...  # one named case
go test -count=1 ./...            # no cache when proving a claim
go test -tags=integration ./...
go test -fuzz=FuzzName ./...
go test -bench=. -benchmem ./...

Roles

Workers do not bypass security: Roles. A green go test is not a security clear of this skill home.

Red flags

• “I’ll assert the mock was called and call it covered”
• “Share one assert across the table — cleaner”
• “It only fails under -count=1 / -race / -shuffle=on, so ignore it”
• “Sleep(10ms) makes it stable”
• “Install gotests / the samber pack to write Go tests”
• “Copy evals or clawhub so we can score the skill”

Stop. Name the case. Assert the contract. Run fresh evidence.

Upstream pin

samber/cc-skills-golang skills/golang-testing @ 22c58a55a0a799b901aa251172923180bad9e010 (MIT). Body is a compress of SKILL.md only. See SOURCES.md.