1 files changed, 87 insertions, 0 deletions
diff --git a/src/internal/singleflight/singleflight_test.go b/src/internal/singleflight/singleflight_test.go
new file mode 100644
index 0000000..c231037
--- /dev/null
+++ b/src/internal/singleflight/singleflight_test.go
@@ -0,0 +1,87 @@
+// Copyright 2013 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 singleflight
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestDo(t *testing.T) {
+	var g Group
+	v, err, _ := g.Do("key", func() (any, error) {
+		return "bar", nil
+	})
+	if got, want := fmt.Sprintf("%v (%T)", v, v), "bar (string)"; got != want {
+		t.Errorf("Do = %v; want %v", got, want)
+	}
+	if err != nil {
+		t.Errorf("Do error = %v", err)
+	}
+}
+
+func TestDoErr(t *testing.T) {
+	var g Group
+	someErr := errors.New("some error")
+	v, err, _ := g.Do("key", func() (any, error) {
+		return nil, someErr
+	})
+	if err != someErr {
+		t.Errorf("Do error = %v; want someErr %v", err, someErr)
+	}
+	if v != nil {
+		t.Errorf("unexpected non-nil value %#v", v)
+	}
+}
+
+func TestDoDupSuppress(t *testing.T) {
+	var g Group
+	var wg1, wg2 sync.WaitGroup
+	c := make(chan string, 1)
+	var calls int32
+	fn := func() (any, error) {
+		if atomic.AddInt32(&calls, 1) == 1 {
+			// First invocation.
+			wg1.Done()
+		}
+		v := <-c
+		c <- v // pump; make available for any future calls
+
+		time.Sleep(10 * time.Millisecond) // let more goroutines enter Do
+
+		return v, nil
+	}
+
+	const n = 10
+	wg1.Add(1)
+	for i := 0; i < n; i++ {
+		wg1.Add(1)
+		wg2.Add(1)
+		go func() {
+			defer wg2.Done()
+			wg1.Done()
+			v, err, _ := g.Do("key", fn)
+			if err != nil {
+				t.Errorf("Do error: %v", err)
+				return
+			}
+			if s, _ := v.(string); s != "bar" {
+				t.Errorf("Do = %T %v; want %q", v, v, "bar")
+			}
+		}()
+	}
+	wg1.Wait()
+	// At least one goroutine is in fn now and all of them have at
+	// least reached the line before the Do.
+	c <- "bar"
+	wg2.Wait()
+	if got := atomic.LoadInt32(&calls); got <= 0 || got >= n {
+		t.Errorf("number of calls = %d; want over 0 and less than %d", got, n)
+	}
+}