Add Context cancellation to clock.

common/clock/systemtimer_test.go

 // 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"
 
+        "golang.org/x/net/context"
+
         . "github.com/smartystreets/goconvey/convey"
 )
 
 func TestSystemTimer(t *testing.T) {
         t.Parallel()
 
         Convey(`A systemTimer instance`, t, func() {
-                t := new(systemTimer)
+                ctx, cancelFunc := context.WithCancel(context.Background())
+                t := GetSystemClock().NewTimer(ctx)
+                defer t.Stop()
 
-                Convey(`Should start with a nil channel.`, func() {
-                        So(t.GetC(), ShouldBeNil)
+                Convey(`Should start with a non-nil channel.`, func() {
+                        So(t.GetC(), ShouldNotBeNil)
                 })
 
                 Convey(`When stopped, should return inactive.`, func() {
                         So(t.Stop(), ShouldBeFalse)
                 })
 
+                Convey(`Will return prematurely if canceled.`, func() {
+                        t.Reset(time.Hour)
+                        cancelFunc()
+                        So((<-t.GetC()).Err, ShouldEqual, context.Canceled)
+                })
+
                 Convey(`When reset`, func() {
                         active := t.Reset(1 * time.Hour)
                         So(active, ShouldBeFalse)
 
                         Convey(`When reset to a short duration`, func() {
                                 // Upper bound of supported platform resolution. Windows is 15ms, so
                                 // make sure we exceed that.
                                 active := t.Reset(100 * time.Millisecond)
 
                                 Convey(`Should return active.`, func() {
@@ skipping 13 matching lines @@
                         })
 
                         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()
-                        })
                 })
         })
 }