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diff --git a/src/python/grpcio_tests/tests/unit/framework/common/test_control.py b/src/python/grpcio_tests/tests/unit/framework/common/test_control.py
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+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Code for instructing systems under test to block or fail."""
+
+import abc
+import contextlib
+import threading
+
+import six
+
+
+class Defect(Exception):
+  """Simulates a programming defect raised into in a system under test.
+
+  Use of a standard exception type is too easily misconstrued as an actual
+  defect in either the test infrastructure or the system under test.
+  """
+
+
+class Control(six.with_metaclass(abc.ABCMeta)):
+  """An object that accepts program control from a system under test.
+
+  Systems under test passed a Control should call its control() method
+  frequently during execution. The control() method may block, raise an
+  exception, or do nothing, all according to the enclosing test's desire for
+  the system under test to simulate hanging, failing, or functioning.
+  """
+
+  @abc.abstractmethod
+  def control(self):
+    """Potentially does anything."""
+    raise NotImplementedError()
+
+
+class PauseFailControl(Control):
+  """A Control that can be used to pause or fail code under control.
+
+  This object is only safe for use from two threads: one of the system under
+  test calling control and the other from the test system calling pause,
+  block_until_paused, and fail.
+  """
+
+  def __init__(self):
+    self._condition = threading.Condition()
+    self._pause = False
+    self._paused = False
+    self._fail = False
+
+  def control(self):
+    with self._condition:
+      if self._fail:
+        raise Defect()
+
+      while self._pause:
+        self._paused = True
+        self._condition.notify_all()
+        self._condition.wait()
+      self._paused = False
+
+  @contextlib.contextmanager
+  def pause(self):
+    """Pauses code under control while controlling code is in context."""
+    with self._condition:
+      self._pause = True
+    yield
+    with self._condition:
+      self._pause = False
+      self._condition.notify_all()
+
+  def block_until_paused(self):
+    """Blocks controlling code until code under control is paused.
+
+    May only be called within the context of a pause call.
+    """
+    with self._condition:
+      while not self._paused:
+        self._condition.wait()
+
+  @contextlib.contextmanager
+  def fail(self):
+    """Fails code under control while controlling code is in context."""
+    with self._condition:
+      self._fail = True
+    yield
+    with self._condition:
+      self._fail = False