Add context-aware "time" library wrapper.

go/src/infra/libs/clock/testclock/testclock.go

Index: go/src/infra/libs/clock/testclock/testclock.go
diff --git a/go/src/infra/libs/clock/testclock/testclock.go b/go/src/infra/libs/clock/testclock/testclock.go
new file mode 100644
index 0000000000000000000000000000000000000000..9aa1f947b792b5b583d6d92d63eaa45a400a5f1d
--- /dev/null
+++ b/go/src/infra/libs/clock/testclock/testclock.go
@@ -0,0 +1,78 @@
+// Copyright (c) 2014 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 testclock
+
+import (
+	"time"
+
+	"golang.org/x/net/context"
+	"infra/libs/clock"
+)
+
+// TestClock is a Clock interface with additional methods to help instrument it.
+type TestClock interface {
+	clock.Clock
+	SetNow(time.Time)
+	SetTimerFactory(TimerFactory)
+}
+
+// testClock is a test-oriented implementation of the 'Clock' interface.
+//
+// This implementation's Clock responses are configurable by modifying its member
+// variables. Time-based events are explicitly triggered by sending on a Timer
+// instance's channel.
+type testClock struct {

[iannucci, 2015/06/02 22:19:03]

mutex for protecting now/timeC/tf

[dnj, 2015/06/03 00:25:28]

Done.

+	now   time.Time      // The current clock time.
+	timeC chan time.Time // Channel to unblock sleeping and After.
+	tf    TimerFactory   // Timer generator function. Must be set to use NewTimer() and After().
+}
+
+// testClock implements clock.TestClock.
+var _ TestClock = (*testClock)(nil)
+
+// New returns a TestClock instance set at the specified time.
+func New(now time.Time, tf TimerFactory) TestClock {
+	return &testClock{
+		now: now,
+		tf:  tf,

[iannucci, 2015/06/02 22:19:03]

timeC?

[dnj, 2015/06/03 00:25:28]

Acknowledged.

+	}
+}
+
+func (c *testClock) Now() time.Time {
+	return c.now
+}
+
+func (c *testClock) Sleep(time.Duration) {
+	if c.timeC != nil {
+		// Wait for sleep signal; update current time.
+		c.now = <-c.timeC
+	}
+}
+
+func (c *testClock) NewTimer() clock.Timer {
+	if c.tf == nil {
+		panic("No test timer generator is configured.")
+	}
+	return c.tf()
+}
+
+func (c *testClock) After(d time.Duration) <-chan time.Time {
+	t := c.NewTimer()
+	t.Reset(d)
+	return t.GetC()
+}
+
+func (c *testClock) SetNow(t time.Time) {
+	c.now = t
+}
+
+func (c *testClock) SetTimerFactory(tf TimerFactory) {
+	c.tf = tf
+}
+
+// Set creates a new Context using the supplied clock instance.
+func Set(ctx context.Context, now time.Time, tf TimerFactory) context.Context {
+	return clock.SetClock(ctx, New(now, tf))
+}