Unrelated test failure, as far as I can tell :-/ Nothing obviously wrong with maasserver.api.tests.test_node.TestPowerMixin.test_POST_test_tests_machine, I haven't been able to reproduce the failure locally, but it broke like so:

======================================================================
ERROR: maasserver.api.tests.test_node.TestPowerMixin.test_POST_test_tests_machine(user=user,client=oauth)
----------------------------------------------------------------------
Traceback (most recent call last):
testtools.testresult.real._StringException: Empty attachments:
  Twisted logs

Traceback (most recent call last):
  File "/tmp/tarmac/branch.a_baMO/src/maastesting/runtest.py", line 134, in _run_user
    result = function(*args, **kwargs)
  File "/home/ubuntu/.buildout/eggs/testtools-2.2.0-py3.5.egg/testtools/testcase.py", line 719, in _run_test_method
    return self._get_test_method()()
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/api/tests/test_node.py", line 556, in test_POST_test_tests_machine
    response = self.client.post(self.get_node_uri(node), {'op': 'test'})
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 512, in post
    secure=secure, **extra)
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 313, in post
    secure=secure, **extra)
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 379, in generic
    return self.request(**r)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/testing/testclient.py", line 140, in request
    return super(MAASSensibleOAuthClient, self).request(**kwargs)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/testing/testclient.py", line 49, in request
    return upcall(**request)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/utils/orm.py", line 562, in __exit__
    self.fire()
  File "/tmp/tarmac/branch.a_baMO/src/provisioningserver/utils/twisted.py", line 225, in wrapper
    result = func(*args, **kwargs)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/utils/async.py", line 218, in fire
    self._fire_in_reactor(hook).wait(LONGTIME)
  File "/usr/lib/python3/dist-packages/crochet/_eventloop.py", line 231, in wait
    result.raiseException()
  File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 368, in raiseException
    raise self.value.with_traceback(self.tb)
maasserver.models.node.DoesNotExist: Node matching query does not exist.

-------------------- >> begin captured logging << --------------------
maas.node: info: I5NT0fKaf40Y9ktd3YN5: Status transition from DEPLOYED to TESTING
maas.node: error: I5NT0fKaf40Y9ktd3YN5: Could not start testing for node: Node matching query does not exist.
--------------------- >> end captured logging << ---------------------
======================================================================
ERROR: maasserver.api.tests.test_node.TestPowerMixin.test_POST_test_tests_machine(user=user,client=user+pass)
----------------------------------------------------------------------
Traceback (most recent call last):
testtools.testresult.real._StringException: Empty attachments:
  Twisted logs

Traceback (most recent call last):
  File "/tmp/tarmac/branch.a_baMO/src/maastesting/runtest.py", line 134, in _run_user
    result = function(*args, **kwargs)
  File "/home/ubuntu/.buildout/eggs/testtools-2.2.0-py3.5.egg/testtools/testcase.py", line 719, in _run_test_method
    return self._get_test_method()()
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/api/tests/test_node.py", line 556, in test_POST_test_tests_machine
    response = self.client.post(self.get_node_uri(node), {'op': 'test'})
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 512, in post
    secure=secure, **extra)
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 313, in post
    secure=secure, **extra)
  File "/usr/lib/python3/dist-packages/django/test/client.py", line 379, in generic
    return self.request(**r)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/testing/testclient.py", line 49, in request
    return upcall(**request)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/utils/orm.py", line 562, in __exit__
    self.fire()
  File "/tmp/tarmac/branch.a_baMO/src/provisioningserver/utils/twisted.py", line 225, in wrapper
    result = func(*args, **kwargs)
  File "/tmp/tarmac/branch.a_baMO/src/maasserver/utils/async.py", line 218, in fire
    self._fire_in_reactor(hook).wait(LONGTIME)
  File "/usr/lib/python3/dist-packages/crochet/_eventloop.py", line 231, in wait
    result.raiseException()
  File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 368, in raiseException
    raise self.value.with_traceback(self.tb)
maasserver.models.node.DoesNotExist: Node matching query does not exist.

-------------------- >> begin captured logging << --------------------
maas.node: info: wg8Rz6kCpvE0UUMFcIYj: Status transition from DEPLOYED to TESTING
maas.node: error: wg8Rz6kCpvE0UUMFcIYj: Could not start testing for node: Node matching query does not exist.
--------------------- >> end captured logging << ---------------------