Fix tab_switching measurement bug.

tools/perf/measurements/tab_switching_unittest.py

+# 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.
+
+from telemetry.core import util
+from telemetry.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 FakePlatform(object):

[eakuefner, 2015/06/18 17:23:29]

Since you're already importing the mock library, can't you also use MagicMock to
replace all of these handwritten mocks?

Also, minor nit: I think 'Fake' is the wrong term here; I like Fowler's summary
of the difference between dummy/fake/mock/stub in this article:
http://martinfowler.com/articles/mocksArentStubs.html . But you can also avoid
these quibbles by using the *ForTest convention that we use in other Telemetry
unit tests.

[deanliao, 2015/06/22 06:37:07]

Except Browser and PageSet, I use MagicMock for the rest classes. Also, I follow
*ForTest convention now.

+  def CanMonitorPower(self):
+    return False
+
+
+class FakeBrowser(object):
+  def __init__(self):
+    self.tabs = []
+    self.platform = FakePlatform()
+
+  def AddTab(self, tab):
+    tab.browser = self
+    self.tabs.append(tab)
+
+
+class FakeTab(object):
+  """Used to mock a browser tab."""

[eakuefner, 2015/06/18 17:23:29]

nit: Why docstring here? It seems like this is as self-explanatory as the rest
of the Fake* classes.

[deanliao, 2015/06/22 06:37:07]

Removed.

+  def __init__(self):
+    self.browser = None
+
+  def HasReachedQuiescence(self):
+    return True
+
+  def Activate(self):
+    pass
+
+
+class FakePage(object):
+  def __init__(self, url):
+    self.url = url
+    self.page_set = None
+
+
+class FakePageSet(object):
+  def __init__(self):
+    self.pages = []
+
+  def AddPage(self, page):
+    page.page_set = self
+    self.pages.append(page)
+
+
+class TabSwitchingUnittest(page_test_test_case.PageTestTestCase):
+  def testIsDone(self):
+    """Tests ValidateAndMeasurePage, specifically _IsDone check."""
+    measure = tab_switching.TabSwitching()
+
+    # For sanity check: #tabs == #page_sets

[eakuefner, 2015/06/18 17:23:29]

Should be #tabs == #pages, right?

[deanliao, 2015/06/22 06:37:07]

Done.

+    page_set = FakePageSet()
+    page_set.AddPage(FakePage('http://fake.com/1'))
+    page_set.AddPage(FakePage('http://fake.com/2'))
+
+    browser = FakeBrowser()
+    tab_0 = FakeTab()
+    tab_1 = FakeTab()
+    browser.AddTab(tab_0)
+    browser.AddTab(tab_1)
+
+    results = page_test_results.PageTestResults()
+
+    # Mock histogram result to test _IsDone really works.
+    mock_get_histogram = mock.MagicMock(side_effect=[
+        # 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}]}',
+        ])
+
+
+    with mock.patch('telemetry.value.histogram_util.GetHistogram',
+                    mock_get_histogram):
+      measure.ValidateAndMeasurePage(page_set.pages[0], tab_1, results)
+      self.assertEqual(8, 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)