How do you write tests that detect goroutine leaks automatically?

Goroutine leaks are among the hardest production bugs to diagnose — they accumulate invisibly. Catching them at test time is far more effective than debugging production memory growth.

import (
    "testing"
    "runtime"
    "time"
    "go.uber.org/goleak"
)

// Method 1: goleak — recommended, most accurate
func TestNoLeak(t *testing.T) {
    defer goleak.VerifyNone(t) // fails if goroutines remain after test

    svc := NewService()
    svc.Start()
    // ... exercise the service ...
    svc.Stop() // if Stop() leaks a goroutine, goleak catches it
}

// goleak with TestMain — check all tests in the package
func TestMain(m *testing.M) {
    goleak.VerifyTestMain(m,
        goleak.IgnoreTopFunction("database/sql.(*DB).connectionOpener"),
    )
}

// Method 2: manual count check (simpler, less precise)
func TestGoroutineCount(t *testing.T) {
    before := runtime.NumGoroutine()

    svc := NewService()
    svc.Start()
    svc.Stop()

    time.Sleep(100 * time.Millisecond) // let goroutines exit
    runtime.Gosched()

    after := runtime.NumGoroutine()
    if after > before {
        buf := make([]byte, 1<<20)
        n := runtime.Stack(buf, true)
        t.Errorf("goroutine leak: %d before, %d after\n%s",
            before, after, buf[:n])
    }
}

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