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.

Note that https://github.com/openstack/charms.openstack is used during tests
and he need `mock`, unfortunatelly it doesn't declare `mock` in its
requirements so it retrieve mock from other charm project (cross dependency).
So we depend on charms.openstack first and when
Ib1ed5b598a52375e29e247db9ab4786df5b6d142 will be merged then CI
will pass without errors.

Depends-On: Ib1ed5b598a52375e29e247db9ab4786df5b6d142
Change-Id: Id925078c5c04c2f89a570bdf7171c666839f9e40

.zuul.yaml

@@ -1,5 +1,4 @@
 - project:
     templates:
-      - python35-charm-jobs
       - openstack-python3-ussuri-jobs
       - openstack-cover-jobs

test-requirements.txt

@@ -13,11 +13,6 @@ setuptools<50.0.0  # https://github.com/pypa/setuptools/commit/04e3df22df840c6bb
 
 requests>=2.18.4
 
-# Newer mock seems to have some syntax which is newer than python3.5 (e.g.
-# f'{something}'
-mock>=1.2,<4.0.0; python_version < '3.6'
-mock>=1.2; python_version >= '3.6'
-
 stestr>=2.2.0
 
 # Dependency of stestr. Workaround for

unit_tests/__init__.py

@@ -14,7 +14,7 @@
 
 import os
 import sys
-import mock
+from unittest import mock
 
 # python-apt is not installed as part of test-requirements but is imported by
 # some charmhelpers modules so create a fake import.

unit_tests/test_actions.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import mock
+from unittest import mock
 
 from unit_tests.test_utils import (
     CharmTestCase,

unit_tests/test_actions_openstack_upgrade.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from mock import patch
+from unittest.mock import patch
 from unit_tests.test_utils import CharmTestCase
 
 import charmhelpers.core.unitdata

unit_tests/test_nova_cc_contexts.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import json
-import mock
+from unittest import mock
 
 import hooks.nova_cc_context as context
 

unit_tests/test_nova_cc_hooks.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from mock import MagicMock, patch, call
+from unittest.mock import MagicMock, patch, call
 import os
 import tempfile
 

unit_tests/test_nova_cc_utils.py

@@ -13,10 +13,9 @@
 # limitations under the License.
 
 from collections import OrderedDict
-from mock import patch, MagicMock, call
 import subprocess
-
 import charmhelpers.core.unitdata
+from unittest.mock import patch, MagicMock, call
 
 from unit_tests.test_utils import (
     CharmTestCase,

unit_tests/test_utils.py

@@ -21,7 +21,7 @@ import unittest
 import yaml
 
 from contextlib import contextmanager
-from mock import patch, MagicMock
+from unittest.mock import patch, MagicMock
 
 
 def load_config():