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diff --git a/src/python/_framework/base/interfaces_test.py b/src/python/_framework/base/interfaces_test.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.
+
+"""Abstract tests against the interfaces of the base layer of RPC Framework."""
+
+import threading
+import time
+
+from _framework.base import interfaces
+from _framework.base import util
+from _framework.foundation import stream
+from _framework.foundation import stream_testing
+from _framework.foundation import stream_util
+
+TICK = 0.1
+SMALL_TIMEOUT = TICK * 50
+STREAM_LENGTH = 100
+
+SYNCHRONOUS_ECHO = 'synchronous echo'
+ASYNCHRONOUS_ECHO = 'asynchronous echo'
+IMMEDIATE_FAILURE = 'immediate failure'
+TRIGGERED_FAILURE = 'triggered failure'
+WAIT_ON_CONDITION = 'wait on condition'
+
+EMPTY_OUTCOME_DICT = {
+    interfaces.COMPLETED: 0,
+    interfaces.CANCELLED: 0,
+    interfaces.EXPIRED: 0,
+    interfaces.RECEPTION_FAILURE: 0,
+    interfaces.TRANSMISSION_FAILURE: 0,
+    interfaces.SERVICER_FAILURE: 0,
+    interfaces.SERVICED_FAILURE: 0,
+    }
+
+
+def _synchronous_echo(output_consumer):
+  return stream_util.TransformingConsumer(lambda x: x, output_consumer)
+
+
+class AsynchronousEcho(stream.Consumer):
+  """A stream.Consumer that echoes its input to another stream.Consumer."""
+
+  def __init__(self, output_consumer, pool):
+    self._lock = threading.Lock()
+    self._output_consumer = output_consumer
+    self._pool = pool
+
+    self._queue = []
+    self._spinning = False
+
+  def _spin(self, value, complete):
+    while True:
+      if value:
+        if complete:
+          self._output_consumer.consume_and_terminate(value)
+        else:
+          self._output_consumer.consume(value)
+      elif complete:
+        self._output_consumer.terminate()
+      with self._lock:
+        if self._queue:
+          value, complete = self._queue.pop(0)
+        else:
+          self._spinning = False
+          return
+
+  def consume(self, value):
+    with self._lock:
+      if self._spinning:
+        self._queue.append((value, False))
+      else:
+        self._spinning = True
+        self._pool.submit(self._spin, value, False)
+
+  def terminate(self):
+    with self._lock:
+      if self._spinning:
+        self._queue.append((None, True))
+      else:
+        self._spinning = True
+        self._pool.submit(self._spin, None, True)
+
+  def consume_and_terminate(self, value):
+    with self._lock:
+      if self._spinning:
+        self._queue.append((value, True))
+      else:
+        self._spinning = True
+        self._pool.submit(self._spin, value, True)
+
+
+class TestServicer(interfaces.Servicer):
+  """An interfaces.Servicer with instrumented for testing."""
+
+  def __init__(self, pool):
+    self._pool = pool
+    self.condition = threading.Condition()
+    self._released = False
+
+  def service(self, name, context, output_consumer):
+    if name == SYNCHRONOUS_ECHO:
+      return _synchronous_echo(output_consumer)
+    elif name == ASYNCHRONOUS_ECHO:
+      return AsynchronousEcho(output_consumer, self._pool)
+    elif name == IMMEDIATE_FAILURE:
+      raise ValueError()
+    elif name == TRIGGERED_FAILURE:
+      raise NotImplementedError
+    elif name == WAIT_ON_CONDITION:
+      with self.condition:
+        while not self._released:
+          self.condition.wait()
+      return _synchronous_echo(output_consumer)
+    else:
+      raise NotImplementedError()
+
+  def release(self):
+    with self.condition:
+      self._released = True
+      self.condition.notify_all()
+
+
+class EasyServicedIngestor(interfaces.ServicedIngestor):
+  """A trivial implementation of interfaces.ServicedIngestor."""
+
+  def __init__(self, consumer):
+    self._consumer = consumer
+
+  def consumer(self, operation_context):
+    """See interfaces.ServicedIngestor.consumer for specification."""
+    return self._consumer
+
+
+class FrontAndBackTest(object):
+  """A test suite usable against any joined Front and Back."""
+
+  # Pylint doesn't know that this is a unittest.TestCase mix-in.
+  # pylint: disable=invalid-name
+
+  def testSimplestCall(self):
+    """Tests the absolute simplest call - a one-packet fire-and-forget."""
+    self.front.operate(
+        SYNCHRONOUS_ECHO, None, True, SMALL_TIMEOUT,
+        util.none_serviced_subscription(), 'test trace ID')
+    util.wait_for_idle(self.front)
+    self.assertEqual(1, self.front.operation_stats()[interfaces.COMPLETED])
+
+    # Assuming nothing really pathological (such as pauses on the order of
+    # SMALL_TIMEOUT interfering with this test) there are a two different ways
+    # the back could have experienced execution up to this point:
+    # (1) The packet is still either in the front waiting to be transmitted
+    # or is somewhere on the link between the front and the back. The back has
+    # no idea that this test is even happening. Calling wait_for_idle on it
+    # would do no good because in this case the back is idle and the call would
+    # return with the packet bound for it still in the front or on the link.
+    back_operation_stats = self.back.operation_stats()
+    first_back_possibility = EMPTY_OUTCOME_DICT
+    # (2) The packet arrived at the back and the back completed the operation.
+    second_back_possibility = dict(EMPTY_OUTCOME_DICT)
+    second_back_possibility[interfaces.COMPLETED] = 1
+    self.assertIn(
+        back_operation_stats, (first_back_possibility, second_back_possibility))
+    # It's true that if the packet had arrived at the back and the back had
+    # begun processing that wait_for_idle could hold test execution until the
+    # back completed the operation, but that doesn't really collapse the
+    # possibility space down to one solution.
+
+  def testEntireEcho(self):
+    """Tests a very simple one-packet-each-way round-trip."""
+    test_payload = 'test payload'
+    test_consumer = stream_testing.TestConsumer()
+    subscription = util.full_serviced_subscription(
+        EasyServicedIngestor(test_consumer))
+
+    self.front.operate(
+        ASYNCHRONOUS_ECHO, test_payload, True, SMALL_TIMEOUT, subscription,
+        'test trace ID')
+
+    util.wait_for_idle(self.front)
+    util.wait_for_idle(self.back)
+    self.assertEqual(1, self.front.operation_stats()[interfaces.COMPLETED])
+    self.assertEqual(1, self.back.operation_stats()[interfaces.COMPLETED])
+    self.assertListEqual([(test_payload, True)], test_consumer.calls)
+
+  def testBidirectionalStreamingEcho(self):
+    """Tests sending multiple packets each way."""
+    test_payload_template = 'test_payload: %03d'
+    test_payloads = [test_payload_template % i for i in range(STREAM_LENGTH)]
+    test_consumer = stream_testing.TestConsumer()
+    subscription = util.full_serviced_subscription(
+        EasyServicedIngestor(test_consumer))
+
+    operation = self.front.operate(
+        SYNCHRONOUS_ECHO, None, False, SMALL_TIMEOUT, subscription,
+        'test trace ID')
+
+    for test_payload in test_payloads:
+      operation.consumer.consume(test_payload)
+    operation.consumer.terminate()
+
+    util.wait_for_idle(self.front)
+    util.wait_for_idle(self.back)
+    self.assertEqual(1, self.front.operation_stats()[interfaces.COMPLETED])
+    self.assertEqual(1, self.back.operation_stats()[interfaces.COMPLETED])
+    self.assertListEqual(test_payloads, test_consumer.values())
+
+  def testCancellation(self):
+    """Tests cancelling a long-lived operation."""
+    test_consumer = stream_testing.TestConsumer()
+    subscription = util.full_serviced_subscription(
+        EasyServicedIngestor(test_consumer))
+
+    operation = self.front.operate(
+        ASYNCHRONOUS_ECHO, None, False, SMALL_TIMEOUT, subscription,
+        'test trace ID')
+    operation.cancel()
+
+    util.wait_for_idle(self.front)
+    self.assertEqual(1, self.front.operation_stats()[interfaces.CANCELLED])
+    util.wait_for_idle(self.back)
+    self.assertListEqual([], test_consumer.calls)
+
+    # Assuming nothing really pathological (such as pauses on the order of
+    # SMALL_TIMEOUT interfering with this test) there are a two different ways
+    # the back could have experienced execution up to this point:
+    # (1) Both packets are still either in the front waiting to be transmitted
+    # or are somewhere on the link between the front and the back. The back has
+    # no idea that this test is even happening. Calling wait_for_idle on it
+    # would do no good because in this case the back is idle and the call would
+    # return with the packets bound for it still in the front or on the link.
+    back_operation_stats = self.back.operation_stats()
+    first_back_possibility = EMPTY_OUTCOME_DICT
+    # (2) Both packets arrived within SMALL_TIMEOUT of one another at the back.
+    # The back started processing based on the first packet and then stopped
+    # upon receiving the cancellation packet.
+    second_back_possibility = dict(EMPTY_OUTCOME_DICT)
+    second_back_possibility[interfaces.CANCELLED] = 1
+    self.assertIn(
+        back_operation_stats, (first_back_possibility, second_back_possibility))
+
+  def testExpiration(self):
+    """Tests that operations time out."""
+    timeout = TICK * 2
+    allowance = TICK  # How much extra time to
+    condition = threading.Condition()
+    test_payload = 'test payload'
+    subscription = util.termination_only_serviced_subscription()
+    start_time = time.time()
+
+    outcome_cell = [None]
+    termination_time_cell = [None]
+    def termination_action(outcome):
+      with condition:
+        outcome_cell[0] = outcome
+        termination_time_cell[0] = time.time()
+        condition.notify()
+
+    with condition:
+      operation = self.front.operate(
+          SYNCHRONOUS_ECHO, test_payload, False, timeout, subscription,
+          'test trace ID')
+      operation.context.add_termination_callback(termination_action)
+      while outcome_cell[0] is None:
+        condition.wait()
+
+    duration = termination_time_cell[0] - start_time
+    self.assertLessEqual(timeout, duration)
+    self.assertLess(duration, timeout + allowance)
+    self.assertEqual(interfaces.EXPIRED, outcome_cell[0])
+    util.wait_for_idle(self.front)
+    self.assertEqual(1, self.front.operation_stats()[interfaces.EXPIRED])
+    util.wait_for_idle(self.back)
+    self.assertLessEqual(1, self.back.operation_stats()[interfaces.EXPIRED])