Added metrics to track the time between task switches done via the shelf.

ash/metrics/task_switch_time_tracker_unittest.cc

Index: ash/metrics/task_switch_time_tracker_unittest.cc
diff --git a/ash/metrics/task_switch_time_tracker_unittest.cc b/ash/metrics/task_switch_time_tracker_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7fc3aba928305447e5c9890ff9d23fb537efbdff
--- /dev/null
+++ b/ash/metrics/task_switch_time_tracker_unittest.cc
@@ -0,0 +1,107 @@
+// 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.
+
+#include "ash/metrics/task_switch_time_tracker.h"
+
+#include <string>
+
+#include "ash/test/task_switch_time_tracker_test_api.h"
+#include "base/test/histogram_tester.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace ash {
+
+namespace {
+
+// A dummy histogram name.
+const std::string kHistogramName = "Dummy.Histogram";
+
+}  // namespace
+
+class TaskSwitchTimeTrackerTest : public testing::Test {
+ public:
+  TaskSwitchTimeTrackerTest();
+  ~TaskSwitchTimeTrackerTest() override;
+
+  // testing::Test:
+  void SetUp() override;
+  void TearDown() override;
+
+  // Wrapper to the test targets OnTaskSwitch() method.
+  void OnTaskSwitch();
+
+  TaskSwitchTimeTracker* time_tracker() {
+    return time_tracker_test_api_->time_tracker();
+  }
+
+ protected:
+  // Used to verify recorded histogram data.
+  scoped_ptr<base::HistogramTester> histogram_tester_;
+
+  // A Test API that wraps the test target.
+  scoped_ptr<test::TaskSwitchTimeTrackerTestAPI> time_tracker_test_api_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TaskSwitchTimeTrackerTest);
+};
+
+TaskSwitchTimeTrackerTest::TaskSwitchTimeTrackerTest() {
+}
+
+TaskSwitchTimeTrackerTest::~TaskSwitchTimeTrackerTest() {
+}
+
+void TaskSwitchTimeTrackerTest::SetUp() {
+  testing::Test::SetUp();
+
+  histogram_tester_.reset(new base::HistogramTester());
+  time_tracker_test_api_.reset(
+      new test::TaskSwitchTimeTrackerTestAPI(kHistogramName));
+  // The TaskSwitchTimeTracker interprets a value of base::TimeTicks() as if the
+  // |last_action_time_| has not been set.
+  time_tracker_test_api_->Advance(base::TimeDelta::FromMilliseconds(1));
+}
+
+void TaskSwitchTimeTrackerTest::TearDown() {
+  testing::Test::TearDown();
+  time_tracker_test_api_.reset();
+  histogram_tester_.reset();
+}
+
+void TaskSwitchTimeTrackerTest::OnTaskSwitch() {
+  time_tracker()->OnTaskSwitch();
+}
+
+// Verifies TaskSwitchTimeTracker::HasLastActionTime() returns false after
+// construction.
+TEST_F(TaskSwitchTimeTrackerTest,
+       HasLastActionTimeShouldBeFalseAfterConstruction) {
+  EXPECT_FALSE(time_tracker_test_api_->HasLastActionTime());
+}
+
+// Verifies TaskSwitchTimeTracker::HasLastActionTime() returns true after the
+// first call to TaskSwitchTimeTracker::OnTaskSwitch() and no histogram data was
+// recorded.
+TEST_F(TaskSwitchTimeTrackerTest,
+       HasLastActionTimeShouldBeTrueAfterOnTaskSwitch) {
+  OnTaskSwitch();
+  histogram_tester_->ExpectTotalCount(kHistogramName, 0);
+}
+
+// Verfies that the histogram data is recorded in the correct buckets.
+TEST_F(TaskSwitchTimeTrackerTest, RecordAfterTwoTaskSwitches) {
+  OnTaskSwitch();
+
+  time_tracker_test_api_->Advance(base::TimeDelta::FromMilliseconds(2));
+  OnTaskSwitch();
+  histogram_tester_->ExpectTotalCount(kHistogramName, 1);
+  histogram_tester_->ExpectBucketCount(kHistogramName, 0, 1);
+
+  time_tracker_test_api_->Advance(base::TimeDelta::FromSeconds(1));
+  OnTaskSwitch();
+  histogram_tester_->ExpectTotalCount(kHistogramName, 2);
+  histogram_tester_->ExpectBucketCount(kHistogramName, 1, 1);
+}
+
+}  // namespace ash