Android gtest runner: Only query device for test list when necessary

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 9369959ed2af3e17900d073976d8106356a15d50..94c80240abfebcdff7c23f981bf84b621201235c 100644
--- a/build/android/pylib/local/device/local_device_gtest_run.py
+++ b/build/android/pylib/local/device/local_device_gtest_run.py
@@ -52,6 +52,32 @@ def PullAppFilesImpl(device, package, files, directory):
         break
     device.PullFile(device_file, host_file)
 
+
+def _ExtractTestsFromFilter(gtest_filter):

[jbudorick, 2015/10/08 15:01:46]

It's hard for me to describe why, but this whole mechanism feels like a code
smell. I think I see what you're trying to do, but I'm not sure this is the
right way to accomplish it.

[agrieve, 2015/10/08 15:59:47]

Yeah, I had at first just cached the test list like instrumentation tests do,
but then realized the cache would be invalidated each time you re-built the
test, which is pretty much every time when you're trying to fix / debug a test.

I think it'd be fine to remove the .* case since that's the opinionated one, but
I have already used it to run a set of failing tests before so wanted to add it
in.

+  """Returns the list of tests specified by the given filter.
+
+  Returns:
+    None if the device should be queried for the test list instead.
+  """
+  # Empty means all tests, - means exclude filter.
+  if not gtest_filter or '-' in gtest_filter:
+    return None
+
+  patterns = gtest_filter.split(':')
+  # For a single pattern, allow it even if it has a wildcard so long as the
+  # wildcard comes at the end and there is at least one . to prove the scope is
+  # not too large.
+  # This heuristic is not necessarily faster, but normally is.
+  if len(patterns) == 1 and patterns[0].endswith('*'):
+    no_suffix = patterns[0].rstrip('*')
+    if '*' not in no_suffix and '.' in no_suffix:
+      return patterns
+
+  if '*' in gtest_filter:
+    return None
+  return patterns
+
+
 class _ApkDelegate(object):
   def __init__(self, test_instance):
     self._activity = test_instance.activity
@@ -229,8 +255,17 @@ class LocalDeviceGtestRun(local_device_test_run.LocalDeviceTestRun):
       tests = self._test_instance.FilterTests(tests)
       return tests
 
-    # Result should be the same for all devices, so just use the first one.
-    return list_tests(self._env.devices[0])
+    # When there's only one device, it still makes sense to retrieve the test
+    # list since test output is not retrieve until after the test completes.

[jbudorick, 2015/10/08 15:01:46]

Why do you say that it still makes sense to retrieve the test list with one
device, but not if the filter matches some set of heuristics?

also, nit: retrieved

[agrieve, 2015/10/08 15:59:46]

Clarified (but not 100% sure it's even the case, so please tell me if it's
wrong)

+    gtest_filter = self._test_instance.gtest_filter
+    # But when running only a single test, skip querying the device (which
+    # takes ~3 seconds).
+    tests = _ExtractTestsFromFilter(gtest_filter)
+
+    if not tests:
+      # Result should be the same for all devices, so just use the first one.
+      tests = list_tests(self._env.devices[0])
+    return tests
 
   #override
   def _RunTest(self, device, test):