Use unittest.mock instead of mock

The mock third party library was needed for mock support in py2
runtimes. Since we now only support py36 and later, we can use the
standard lib unittest.mock module instead.

Also enabled the hacking check that should have caught this, it
was missing from tox.ini along with most of the other in-tree
hacking checks we have added over the years.

Change-Id: Id91175d0db8b8edc72f0dd98925ddbf7415bb881

HACKING.rst

@@ -26,6 +26,8 @@ Below you can find a list of checks specific to this repository.
 - [N343] Production code must not import from neutron.tests.*
 - [N344] Python 3: Do not use filter(lambda obj: test(obj), data). Replace it
   with [obj for obj in data if test(obj)].
+- [N346] Use neutron_lib.db.api.sqla_listen rather than sqlalchemy
+- [N347] Test code must not import mock library
 
 .. note::
    When adding a new hacking check to this repository or ``neutron-lib``, make

lower-constraints.txt

@@ -44,7 +44,6 @@ logilab-common==1.4.1
 logutils==0.3.5
 Mako==0.4.0
 MarkupSafe==1.0
-mock==3.0.0
 monotonic==0.6;python_version<'3.3'
 mox3==0.20.0
 msgpack-python==0.4.0

neutron/tests/unit/common/ovn/test_utils.py

@@ -13,8 +13,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from unittest import mock
+
 import fixtures
-import mock
 from neutron_lib.api.definitions import extra_dhcp_opt as edo_ext
 
 from neutron.common.ovn import constants

tox.ini

@@ -172,8 +172,17 @@ import-order-style = pep8
 [flake8:local-plugins]
 extension =
   # Checks specific to neutron repo
+  N322 = neutron.hacking.checks:check_assert_called_once_with
+  N328 = neutron.hacking.checks:check_asserttruefalse
+  N330 = neutron.hacking.checks:check_assertempty
+  N331 = neutron.hacking.checks:check_assertisinstance
+  N332 = neutron.hacking.checks:check_assertequal_for_httpcode
   N340 = neutron.hacking.checks:check_oslo_i18n_wrapper
   N341 = neutron.hacking.checks:check_builtins_gettext
+  N343 = neutron.hacking.checks:check_no_imports_from_tests
+  N344 = neutron.hacking.checks:check_python3_no_filter
+  N346 = neutron.hacking.checks:check_no_sqlalchemy_event_import
+  N347 = neutron.hacking.checks:check_no_import_mock
   # Checks from neutron-lib
   N521 = neutron_lib.hacking.checks:use_jsonutils
   N524 = neutron_lib.hacking.checks:check_no_contextlib_nested