Fixes exit code when there are no host-driven tests

build/android/test_runner.py

 #!/usr/bin/env python
 #
 # Copyright 2013 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.
 
 """Runs all types of tests from one unified interface.
 
 TODO(gkanwar):
 * Add options to run Monkey tests.
@@ skipping 418 matching lines @@
         test_timeout=None,
         num_retries=options.num_retries)
 
     results.AddTestRunResults(test_results)
 
   if options.run_python_tests:
     runner_factory, tests = host_driven_setup.InstrumentationSetup(
         options.python_test_root, options.official_build,
         instrumentation_options)
 
-    test_results, test_exit_code = test_dispatcher.RunTests(
-        tests, runner_factory, False,
-        options.test_device,
-        shard=True,
-        build_type=options.build_type,
-        test_timeout=None,
-        num_retries=options.num_retries)
+    if tests:
+      test_results, test_exit_code = test_dispatcher.RunTests(
+          tests, runner_factory, False,
+          options.test_device,
+          shard=True,
+          build_type=options.build_type,
+          test_timeout=None,
+          num_retries=options.num_retries)
 
-    results.AddTestRunResults(test_results)
+      results.AddTestRunResults(test_results)
 
-    # Only allow exit code escalation
-    if test_exit_code and exit_code != constants.ERROR_EXIT_CODE:
-      exit_code = test_exit_code
+      # Only allow exit code escalation
+      if test_exit_code and exit_code != constants.ERROR_EXIT_CODE:
+        exit_code = test_exit_code
 
   report_results.LogFull(
       results=results,
       test_type='Instrumentation',
       test_package=os.path.basename(options.test_apk),
       annotation=options.annotations,
       build_type=options.build_type,
       flakiness_server=options.flakiness_dashboard_server)
 
   return exit_code
@@ skipping 154 matching lines @@
     return 0
   command = argv[1]
   VALID_COMMANDS[command].add_options_func(option_parser)
   options, args = option_parser.parse_args(argv)
   return VALID_COMMANDS[command].run_command_func(
       command, options, args, option_parser)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))