1 files changed, 79 insertions, 0 deletions
diff --git a/src/cmd/go/internal/par/queue_test.go b/src/cmd/go/internal/par/queue_test.go
new file mode 100644
index 0000000000..1331e65f98
--- /dev/null
+++ b/src/cmd/go/internal/par/queue_test.go
@@ -0,0 +1,79 @@
+// Copyright 2020 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 par
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestQueueIdle(t *testing.T) {
+	q := NewQueue(1)
+	select {
+	case <-q.Idle():
+	default:
+		t.Errorf("NewQueue(1) is not initially idle.")
+	}
+
+	started := make(chan struct{})
+	unblock := make(chan struct{})
+	q.Add(func() {
+		close(started)
+		<-unblock
+	})
+
+	<-started
+	idle := q.Idle()
+	select {
+	case <-idle:
+		t.Errorf("NewQueue(1) is marked idle while processing work.")
+	default:
+	}
+
+	close(unblock)
+	<-idle // Should be closed as soon as the Add callback returns.
+}
+
+func TestQueueBacklog(t *testing.T) {
+	const (
+		maxActive = 2
+		totalWork = 3 * maxActive
+	)
+
+	q := NewQueue(maxActive)
+	t.Logf("q = NewQueue(%d)", maxActive)
+
+	var wg sync.WaitGroup
+	wg.Add(totalWork)
+	started := make([]chan struct{}, totalWork)
+	unblock := make(chan struct{})
+	for i := range started {
+		started[i] = make(chan struct{})
+		i := i
+		q.Add(func() {
+			close(started[i])
+			<-unblock
+			wg.Done()
+		})
+	}
+
+	for i, c := range started {
+		if i < maxActive {
+			<-c // Work item i should be started immediately.
+		} else {
+			select {
+			case <-c:
+				t.Errorf("Work item %d started before previous items finished.", i)
+			default:
+			}
+		}
+	}
+
+	close(unblock)
+	for _, c := range started[maxActive:] {
+		<-c
+	}
+	wg.Wait()
+}