Improve platform mocking

Patch out charmhelpers.osplatform.get_platform() and
charmhelpers.core.host.lsb_release() globally in the unit tests to
insulate the unit tests from the platform that the unit tests are being
run on.

Copied from
https://review.opendev.org/c/openstack/charm-cinder-backup/+/899200

Change-Id: Ibb36344b1c30492b8a822fb48f753c6bdf6ca279

tox.ini

@@ -44,52 +44,61 @@ commands =
 
 [testenv:py35]
 basepython = python3.5
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:py36]
 basepython = python3.6
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:py37]
 basepython = python3.7
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:py38]
 basepython = python3.8
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+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
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:py310]
 basepython = python3.10
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:py3]
 basepython = python3
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:pep8]
 basepython = python3
-deps = flake8==3.9.2
-       charm-tools==2.8.4
+deps =
+    flake8==3.9.2
+    git+https://github.com/juju/charm-tools.git
 commands = flake8 {posargs} hooks unit_tests tests actions lib files
            charm-proof
 
 [testenv:cover]
 # Technique based heavily upon
 # https://github.com/openstack/nova/blob/master/tox.ini
 basepython = python3
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps =
+    -r{toxinidir}/requirements.txt
+    -r{toxinidir}/test-requirements.txt
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run

unit_tests/__init__.py

@@ -14,6 +14,7 @@
 
 import os
 import sys
+from unittest.mock import patch
 
 _path = os.path.dirname(os.path.realpath(__file__))
 _actions = os.path.abspath(os.path.join(_path, '../actions'))
@@ -31,3 +32,16 @@ def _add_path(path):
 _add_path(_hooks)
 _add_path(_charmhelpers)
 _add_path(_unit_tests)
+
+
+# Patch out lsb_release() and get_platform() as unit tests should be fully
+# insulated from the underlying platform.  Unit tests assume that the system is
+# ubuntu jammy.
+patch(
+    'charmhelpers.osplatform.get_platform', return_value='ubuntu'
+).start()
+patch(
+    'charmhelpers.core.host.lsb_release',
+    return_value={
+        'DISTRIB_CODENAME': 'jammy'
+    }).start()