1 files changed, 68 insertions, 0 deletions
diff --git a/src/sync/once_test.go b/src/sync/once_test.go
new file mode 100644
index 000000000..1eec8d18e
--- /dev/null
+++ b/src/sync/once_test.go
@@ -0,0 +1,68 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync_test
+
+import (
+	. "sync"
+	"testing"
+)
+
+type one int
+
+func (o *one) Increment() {
+	*o++
+}
+
+func run(t *testing.T, once *Once, o *one, c chan bool) {
+	once.Do(func() { o.Increment() })
+	if v := *o; v != 1 {
+		t.Errorf("once failed inside run: %d is not 1", v)
+	}
+	c <- true
+}
+
+func TestOnce(t *testing.T) {
+	o := new(one)
+	once := new(Once)
+	c := make(chan bool)
+	const N = 10
+	for i := 0; i < N; i++ {
+		go run(t, once, o, c)
+	}
+	for i := 0; i < N; i++ {
+		<-c
+	}
+	if *o != 1 {
+		t.Errorf("once failed outside run: %d is not 1", *o)
+	}
+}
+
+func TestOncePanic(t *testing.T) {
+	var once Once
+	func() {
+		defer func() {
+			if r := recover(); r == nil {
+				t.Fatalf("Once.Do did not panic")
+			}
+		}()
+		once.Do(func() {
+			panic("failed")
+		})
+	}()
+
+	once.Do(func() {
+		t.Fatalf("Once.Do called twice")
+	})
+}
+
+func BenchmarkOnce(b *testing.B) {
+	var once Once
+	f := func() {}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			once.Do(f)
+		}
+	})
+}