Check for stray threads from tests and fail if found

testing_support/tests/thread_watcher_test.py

Index: testing_support/tests/thread_watcher_test.py
diff --git a/testing_support/tests/thread_watcher_test.py b/testing_support/tests/thread_watcher_test.py
new file mode 100644
index 0000000000000000000000000000000000000000..7bf5aa62a9afd99ff15b54ad55a05f8fccd83334
--- /dev/null
+++ b/testing_support/tests/thread_watcher_test.py
@@ -0,0 +1,85 @@
+# Copyright 2016 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 re
+import threading
+import time
+import unittest
+
+from testing_support import thread_watcher
+
+class TestNoExtraThreads(thread_watcher.TestCase):
+  def mock_test(self):
+    pass
+
+
+class TestExtraThreads(thread_watcher.TestCase):
+  def _start_thread(self, name='foo'):
+    stop = threading.Event()
+    def thread_func():
+      while not stop.is_set():
+        time.sleep(0.01)
+
+    t = threading.Thread(target=thread_func, name=name)
+    t.start()
+    return t, stop
+
+  def mock_test(self):
+    self.t1, self.stop1 = self._start_thread('foo')
+    self.t2, self.stop2 = self._start_thread('bar')
+
+  def stopThreads(self):
+    self.stop1.set()
+    self.stop2.set()
+    self.t1.join()
+    self.t2.join()
+
+
+class ThreadWatcherTestCase(thread_watcher.TestCase):
+  @mock.patch('unittest.TestCase.fail')
+  def test_no_extra_threads(self, fail_mock):
+    TestNoExtraThreads('mock_test').run()
+    self.assertFalse(fail_mock.called)
+
+  @mock.patch('unittest.TestCase.fail')
+  def test_extra_threads(self, fail_mock):
+    t = TestExtraThreads('mock_test')
+    t.run()
+    t.stopThreads()
+
+    self.assertEqual(len(fail_mock.call_args_list), 1)
+    self.assertEqual(len(fail_mock.call_args_list[0]), 2)
+    self.assertEqual(len(fail_mock.call_args_list[0][0]), 1)
+    self.assertEqual(len(fail_mock.call_args_list[0][1]), 0)
+
+    error_message = fail_mock.call_args_list[0][0][0]
+    self.assertRegexpMatches(
+        error_message,
+        re.compile('^Found 2 running thread\(s\) after the test.\n\n'
+                   'Thread <Thread\(foo, started \d+\)> stacktrace:\n'
+                   '  .*\n\n'
+                   'Thread <Thread\(bar, started \d+\)> stacktrace:\n'
+                   '  .*\n$', re.DOTALL)
+    )
+    self.assertNotIn('  Thread stopped while acquiring stacktrace.\n', error_message)
+
+  @mock.patch('unittest.TestCase.fail')
+  def test_fail_get_stacktrace(self, fail_mock):
+    with mock.patch('sys._current_frames', mock.Mock(return_value={})):
+      t = TestExtraThreads('mock_test')
+      t.run()
+      t.stopThreads()
+
+    self.assertEqual(len(fail_mock.call_args_list), 1)
+    self.assertEqual(len(fail_mock.call_args_list[0]), 2)
+    self.assertEqual(len(fail_mock.call_args_list[0][0]), 1)
+    self.assertEqual(len(fail_mock.call_args_list[0][1]), 0)
+
+    error_message = fail_mock.call_args_list[0][0][0]
+    self.assertIn('  Thread stopped while acquiring stacktrace.\n', error_message)
+
+
+if __name__ == '__main__':
+  unittest.main()