[Telemetry] Test for display tracing

BUG=535731

Review URL: https://codereview.chromium.org/1366133002

Cr-Commit-Position: refs/heads/master@{#351099}

tools/telemetry/telemetry/internal/platform/android_platform_backend.py

@@ -228,9 +228,11 @@ class AndroidPlatformBackend(
     if not self._surface_stats_collector:
       return
 
-    refresh_period, timestamps = self._surface_stats_collector.Stop()
-    pid = self._surface_stats_collector.GetSurfaceFlingerPid()
-    self._surface_stats_collector = None
+    try:
+      refresh_period, timestamps = self._surface_stats_collector.Stop()
+      pid = self._surface_stats_collector.GetSurfaceFlingerPid()
+    finally:
+      self._surface_stats_collector = None
     # TODO(sullivan): should this code be inline, or live elsewhere?
     events = []
     for ts in timestamps:

tools/telemetry/telemetry/internal/platform/tracing_agent/display_tracing_agent_unittest.py

+# Copyright 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.
+import mock
+import unittest
+
+from telemetry.internal.platform import android_platform_backend
+from telemetry.internal.platform.tracing_agent import display_tracing_agent
+from telemetry.timeline import tracing_category_filter
+from telemetry.timeline import tracing_options
+
+# pylint: disable=super-init-not-called,abstract-method
+class FakeAndroidPlatformBackend(
+    android_platform_backend.AndroidPlatformBackend):
+  def __init__(self):
+    self._device = 0
+    self._raw_display_frame_rate_measurements = []
+    self._surface_stats_collector = None
+
+  @property
+  def surface_stats_collector(self):
+    return self._surface_stats_collector
+
+  def IsDisplayTracingSupported(self):
+    return True
+
+
+class DisplayTracingAgentTest(unittest.TestCase):
+  def setUp(self):
+    self._trace_options = tracing_options.TracingOptions()
+    self._trace_options.enable_platform_display_trace = True
+    self._category_filter = tracing_category_filter.TracingCategoryFilter()
+    self._platform_backend = FakeAndroidPlatformBackend()
+    self._agent = display_tracing_agent.DisplayTracingAgent(
+        self._platform_backend)
+
+  @mock.patch(
+      'devil.android.perf.surface_stats_collector.SurfaceStatsCollector')
+  def testStartAndStopTracing(self, MockSurfaceStatsCollector):
+    self._agent.Start(self._trace_options, self._category_filter, 10)
+    # Second start tracing will raise error.
+    with self.assertRaises(AssertionError):
+      self._agent.Start(self._trace_options, self._category_filter, 10)
+    self._platform_backend.surface_stats_collector.Stop.return_value = (0, [])
+    self._agent.Stop(mock.MagicMock())
+
+    # Can start and stop tracing multiple times.
+    self._agent.Start(self._trace_options, self._category_filter, 10)
+    self._platform_backend.surface_stats_collector.Stop.return_value = (0, [])
+    self._agent.Stop(mock.MagicMock())
+
+  @mock.patch(
+      'devil.android.perf.surface_stats_collector.SurfaceStatsCollector')
+  def testExceptionRaisedInStopTracing(self, MockSurfaceStatsCollector):
+    self._agent.Start(self._trace_options, self._category_filter, 10)
+    self._platform_backend.surface_stats_collector.Stop.side_effect = Exception(
+        'Raise error when stopping tracing.')
+    with self.assertRaises(Exception):
+      self._agent.Stop(mock.MagicMock())
+
+    # Tracing is stopped even if there is exception. And the agent can start
+    # tracing again.
+    self._agent.Start(self._trace_options, self._category_filter, 10)
+    self._platform_backend.surface_stats_collector.Stop.side_effect = None
+    self._platform_backend.surface_stats_collector.Stop.return_value = (0, [])
+    self._agent.Stop(mock.MagicMock())