Fix tab_switching measurement bug.

tools/perf/measurements/tab_switching_unittest.py

Index: tools/perf/measurements/tab_switching_unittest.py
diff --git a/tools/perf/measurements/tab_switching_unittest.py b/tools/perf/measurements/tab_switching_unittest.py
new file mode 100644
index 0000000000000000000000000000000000000000..91024f19b6334f6eb6ab2514039247797ffcd32f
--- /dev/null
+++ b/tools/perf/measurements/tab_switching_unittest.py
@@ -0,0 +1,100 @@
+# 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.
+
+import contextlib
+from telemetry.core import util
+from telemetry.internal.results import page_test_results
+from telemetry.unittest_util import page_test_test_case
+
+from measurements import tab_switching
+
+# Import Python mock module (https://pypi.python.org/pypi/mock)
+util.AddDirToPythonPath(util.GetTelemetryDir(), 'third_party', 'mock')
+import mock  # pylint: disable=import-error
+
+
+class BrowserForTest(object):
+  def __init__(self):
+    self.tabs = []
+    self.platform = mock.MagicMock()
+    self.platform.CanMonitorPower = mock.Mock(return_value=False)
+
+  def AddTab(self, tab):
+    tab.browser = self
+    self.tabs.append(tab)
+
+
+class StorySetForTest(object):
+  def __init__(self):
+    self.stories = []
+
+  def AddStory(self, story):
+    story.story_set = self
+    self.stories.append(story)
+
+
+class TabSwitchingUnittest(page_test_test_case.PageTestTestCase):
+  @staticmethod
+  def MakeStoryForTest():
+    story = mock.MagicMock()
+    story.story_set = None
+    return story
+
+  @staticmethod
+  def MakeTabForTest():
+    tab = mock.MagicMock()
+    tab.browser = None
+    tab.HasReachedQuiescence = mock.Mock(return_value=True)
+    return tab
+
+  def testIsDone(self):
+    """Tests ValidateAndMeasurePage, specifically _IsDone check."""
+    measure = tab_switching.TabSwitching()
+
+    # For sanity check: #tabs == #stories
+    story_set = StorySetForTest()
+    story_set.AddStory(self.MakeStoryForTest())
+    story_set.AddStory(self.MakeStoryForTest())
+
+    # Set up a browser with two tabs open
+    browser = BrowserForTest()
+    tab_0 = self.MakeTabForTest()
+    browser.AddTab(tab_0)
+    tab_1 = self.MakeTabForTest()
+    browser.AddTab(tab_1)
+
+    # Mock histogram result to test _IsDone really works.
+    expected_histogram = [
+        # To get first_histogram for last tab (tab_1).
+        '{"count": 0, "buckets": []}',
+        # First _IsDone check for tab_0. Retry.
+        '{"count": 0, "buckets": []}',
+        # Second _IsDone check for tab_0. Retry.
+        '{"count": 0, "buckets": []}',
+        # Third _IsDone check for tab_0. Pass.
+        '{"count": 1, "buckets": [{"low": 1, "high": 2, "count": 1}]}',
+        # To get prev_histogram. End of tab_0 loop.
+        '{"count": 1, "buckets": [{"low": 1, "high": 2, "count": 1}]}',
+        # First _IsDone check for tab_1. Retry.
+        '{"count": 1, "buckets": [{"low": 1, "high": 2, "count": 1}]}',
+        # Second _IsDone check for tab_1. Pass.
+        '{"count": 2, "buckets": [{"low": 1, "high": 2, "count": 1},'
+        '{"low": 2, "high": 3, "count": 1}]}',
+        # To get prev_histogram. End of tab_1 loop.
+        '{"count": 2, "buckets": [{"low": 1, "high": 2, "count": 1},'
+        '{"low": 2, "high": 3, "count": 1}]}',
+        ]
+    mock_get_histogram = mock.MagicMock(side_effect=expected_histogram)
+
+    with contextlib.nested(
+        mock.patch('telemetry.value.histogram_util.GetHistogram',
+                   mock_get_histogram),
+        mock.patch('metrics.keychain_metric.KeychainMetric')):
+      measure.ValidateAndMeasurePage(story_set.stories[0], browser.tabs[-1],
+                                     page_test_results.PageTestResults())
+      self.assertEqual(len(expected_histogram),
+                       len(mock_get_histogram.mock_calls))
+      expected_calls = [mock.call(mock.ANY, mock.ANY, t) for t in
+                        [tab_1] + [tab_0] * 4 + [tab_1] * 3]
+      self.assertEqual(expected_calls, mock_get_histogram.mock_calls)