linux IP lib tests conflicting patches causing sporadic UT failures

[Kevin Benton]

The following failure is happening sporadically when running the unit tests:

ft1.11275: neutron.tests.unit.test_linux_ip_lib.TestDeviceExists.test_device_exists_StringException: Empty attachments:
  pythonlogging:''
  pythonlogging:'neutron.api.extensions'
  stderr
  stdout

Traceback (most recent call last):
  File "neutron/tests/unit/test_linux_ip_lib.py", line 785, in test_device_exists
    _execute.assert_called_once_with('o', 'link', ('show', 'eth0'))
  File "/home/jenkins/workspace/gate-neutron-python27/.tox/py27/local/lib/python2.7/site-packages/mock.py", line 845, in assert_called_once_with
    raise AssertionError(msg)
AssertionError: Expected to be called once. Called 0 times.

[Kevin Benton (kevinbenton)]

The root cause of this is the TestMidonetInterfaceDriver test class. The class it inherits from already patches the 'device_exists' method in ip_lib during setup and then it does it again[1]. Double-patching causes the mock library to fail to stop both patches using the stopall method.

This bug surface after the patch merged that removed all of the explicit addCleanup(patch.stop) methods from unit tests.[2]

1. https://github.com/bigswitch/neutron/blob/1e0ea5217a93fadb915c3dcdf4c260738bed70ac/neutron/tests/unit/test_linux_interface.py#L518

2. https://review.openstack.org/#/c/86538/

[Kevin Benton (kevinbenton)]

Patch here:
https://review.openstack.org/#/c/87097/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/87097
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=e7ca2541b13d9e755f443b866708865ac22a8bd1
Submitter: Jenkins
Branch: master

commit e7ca2541b13d9e755f443b866708865ac22a8bd1
Author: Kevin Benton <email address hidden>
Date: Sat Apr 12 21:27:36 2014 +0000

    Fix dangling patches in Cisco and Midonet tests

    Cisco Nexus Tests:
    Explicitly stops the patch to sys.modules immediately
    after use to fix sporadic failures caused by the patch
    not being handled correctly by mock.patch.stopall.

    Midonet Interface Test:
    Removes the double-patch of the 'device_exists' method
    in ip_lib.

    Closes-Bug: #1307025
    Closes-Bug: #1307038
    Change-Id: Ie22505bb8e406a61e40819d60c76d229916a6e01