Raise exception when all devices fail to list tests.

build/android/pylib/local/device/local_device_gtest_run.py

Index: build/android/pylib/local/device/local_device_gtest_run.py
diff --git a/build/android/pylib/local/device/local_device_gtest_run.py b/build/android/pylib/local/device/local_device_gtest_run.py
index e740f564a23cdb8cb8c52aac216b99421a1d977d..121f351a1cfcd039cbce15cb84a13a3d375fe8e1 100644
--- a/build/android/pylib/local/device/local_device_gtest_run.py
+++ b/build/android/pylib/local/device/local_device_gtest_run.py
@@ -315,6 +315,14 @@ class LocalDeviceGtestRun(local_device_test_run.LocalDeviceTestRun):
 
     # Query all devices in case one fails.
     test_lists = self._env.parallel_devices.pMap(list_tests).pGet(None)
+
+    # If all devices failed to list_tests, raise an exception.
+    check_one_device_failed = lambda result: result == None
+    check_both_devices_failed = lambda device_x_failed, device_y_failed: device_x_failed and device_y_failed
+    if reduce(check_both_devices_failed, map(check_one_device_failed, test_lists)):

[mikecase (-- gone --), 2016/02/19 19:03:42]

You could just do "if all(map(check_one_device_failed, test_lists))" instead of
using reduce.

Also, you could simplify if further and just do something like...

if all([tl is None for tl in test_lists]):
  raise Exception()

^ I think that should work

[BigBossZhiling, 2016/02/19 22:13:47]

Done.

+      # Now we know that all devices failed to do list_tests.
+      raise Exception('Failed to list tests on all devices')

[mikecase (-- gone --), 2016/02/19 19:03:42]

Look around in devil/android/device_errors.py for a more appropriate error.

My guess would do something like raise a device_errors.CommandFailedError

[BigBossZhiling, 2016/02/19 22:13:47]

Done.

+
     # TODO(agrieve): Make this fail rather than return an empty list when
     #     all devices fail.

[mikecase (-- gone --), 2016/02/19 19:03:42]

nit: Remove this TODO.

     return list(sorted(set().union(*[set(tl) for tl in test_lists if tl])))