Add context-aware "time" library wrapper.

go/src/infra/libs/clock/systemtimer_test.go

Index: go/src/infra/libs/clock/systemtimer_test.go
diff --git a/go/src/infra/libs/clock/systemtimer_test.go b/go/src/infra/libs/clock/systemtimer_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..4ab9dfb6dc06f58205dcceec7de72873a7362f65
--- /dev/null
+++ b/go/src/infra/libs/clock/systemtimer_test.go
@@ -0,0 +1,65 @@
+// Copyright 2015 The Chromium 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 clock
+
+import (
+	"testing"
+	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestSystemTimer(t *testing.T) {
+	t.Parallel()
+
+	Convey(`A systemTimer instance`, t, func() {
+		t := new(systemTimer)
+
+		Convey(`Should start with a nil channel.`, func() {
+			So(t.GetC(), ShouldBeNil)
+		})
+
+		Convey(`When stopped, should return inactive.`, func() {
+			So(t.Stop(), ShouldBeFalse)
+		})
+
+		Convey(`When reset`, func() {
+			active := t.Reset(1 * time.Hour)
+			So(active, ShouldBeFalse)
+
+			Convey(`When reset to a short duration`, func() {
+				active := t.Reset(1 * time.Microsecond)
+
+				Convey(`Should return active.`, func() {
+					So(active, ShouldBeTrue)
+				})
+
+				Convey(`Should trigger shortly.`, func() {
+					tm := <-t.GetC()
+					So(tm, ShouldNotResemble, time.Time{})
+				})
+			})
+
+			Convey(`When stopped, should return active and have a non-nil C.`, func() {
+				active := t.Stop()
+				So(active, ShouldBeTrue)
+				So(t.GetC(), ShouldNotBeNil)
+			})
+
+			Convey(`When stopped, should return active.`, func() {
+				active := t.Stop()
+				So(active, ShouldBeTrue)
+			})
+
+			Convey(`Should have a non-nil channel.`, func() {
+				So(t.GetC(), ShouldNotBeNil)
+			})
+
+			Reset(func() {
+				t.Stop()
+			})
+		})
+	})
+}