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.

Change-Id: If62bed2598c42b861a11ceab21e9f1ab0c0cf9dd

.zuul.yaml

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

osci.yaml

@@ -1,6 +1,6 @@
 - project:
     templates:
-      - charm-unit-jobs
+      - charm-yoga-unit-jobs
     check:
       jobs:
       - bionic-octopus
@@ -15,10 +15,9 @@
     parent: func-target
     dependencies:
       - osci-lint
-      - tox-py35
       - tox-py36
-      - tox-py37
       - tox-py38
+      - tox-py39
     vars:
       tox_extra_args: focal
 - job:

test-requirements.txt

@@ -3,7 +3,6 @@
 # requirements management in charms via bot-control.  Thank you.
 charm-tools>=2.4.4
 coverage>=3.6
-mock>=1.2
 flake8>=2.2.4,<=2.4.1
 pyflakes==2.1.1
 stestr>=2.2.0

tox.ini

@@ -57,6 +57,11 @@ basepython = python3.8
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 
+[testenv:py39]
+basepython = python3.9
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
+
 [testenv:py3]
 basepython = python3
 deps = -r{toxinidir}/requirements.txt

unit_tests/__init__.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import sys
-import mock
+import unittest.mock as mock
 
 # Mock out secrets to make py35 happy.
 sys.modules['secrets'] = mock.MagicMock()

unit_tests/test_ceph_dashboard_charm.py

@@ -22,7 +22,7 @@ import sys
 sys.path.append('lib')  # noqa
 sys.path.append('src')  # noqa
 
-from mock import ANY, call, patch, MagicMock
+from unittest.mock import ANY, call, patch, MagicMock
 
 from ops.testing import Harness, _TestingModelBackend
 from ops.model import (