Raise exception when all devices fail to list tests.

build/android/pylib/local/device/local_device_gtest_run.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 collections
 import itertools
 import os
 import posixpath
 
 from devil.android import device_errors
@@ skipping 297 matching lines @@
         on_failure=self._env.BlacklistDevice)
     def list_tests(dev):
       tests = self._delegate.Run(
           None, dev, flags='--gtest_list_tests', timeout=20)
       tests = gtest_test_instance.ParseGTestListTests(tests)
       tests = self._test_instance.FilterTests(tests)
       return tests
 
     # Query all devices in case one fails.
     test_lists = self._env.parallel_devices.pMap(list_tests).pGet(None)
-    # TODO(agrieve): Make this fail rather than return an empty list when
-    #     all devices fail.
+
+    # If all devices failed to list_tests, raise an exception.

[mikecase (-- gone --), 2016/02/19 23:41:53]

super nit: s/list_tests/list tests

[BigBossZhiling, 2016/02/24 22:51:14]

Done.

+    if all([tests == None for tests in test_lists]):

[mikecase (-- gone --), 2016/02/19 23:41:54]

super nit: To match the variable naming below...
s/tests/tl

Also super nit:
"tests is None" is probably more pythonic than "==" None

+      # Now we know that all devices failed to do list_tests.

[mikecase (-- gone --), 2016/02/19 23:41:53]

super nit: Comment is probably unnecessary given you have a comment above
explaining what you are doing.

+      raise device_errors.CommandFailedError(
+          "Failed to list_tests on all devices")

[mikecase (-- gone --), 2016/02/19 23:41:53]

super nit: s/list_tests/list tests
super nit: single quotes (style is single quotes in python unless you have a
single quote in the string)

Also, while I'm being annoying with all my nits. Should probably read (to make
it more clear)...

'Failed to list tests on any device.'
OR
'All devices failed to list tests.'

     return list(sorted(set().union(*[set(tl) for tl in test_lists if tl])))
 
   #override
   def _RunTest(self, device, test):
     # Run the test.
     timeout = (self._test_instance.shard_timeout
                * self.GetTool(device).GetTimeoutScale())
     output = self._delegate.Run(
         test, device, flags=self._test_instance.test_arguments,
         timeout=timeout, retries=0)
@@ skipping 14 matching lines @@
   def TearDown(self):
     @local_device_test_run.handle_shard_failures
     def individual_device_tear_down(dev):
       for s in self._servers.get(str(dev), []):
         s.TearDown()
 
       tool = self.GetTool(dev)
       tool.CleanUpEnvironment()
 
     self._env.parallel_devices.pMap(individual_device_tear_down)