syncs: add new package for extra sync types

syncs/syncs_test.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2020 Tailscale Inc & 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 syncs
+
+import "testing"
+
+func TestWaitGroupChan(t *testing.T) {
+	wg := NewWaitGroupChan()
+
+	wantNotDone := func() {
+		t.Helper()
+		select {
+		case <-wg.DoneChan():
+			t.Fatal("done too early")
+		default:
+		}
+	}
+
+	wantDone := func() {
+		t.Helper()
+		select {
+		case <-wg.DoneChan():
+		default:
+			t.Fatal("expected to be done")
+		}
+	}
+
+	wg.Add(2)
+	wantNotDone()
+
+	wg.Decr()
+	wantNotDone()
+
+	wg.Decr()
+	wantDone()
+	wantDone()
+}
+
+func TestClosedChan(t *testing.T) {
+	ch := ClosedChan()
+	for i := 0; i < 2; i++ {
+		select {
+		case <-ch:
+		default:
+			t.Fatal("not closed")
+		}
+	}
+}