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.

Change-Id: Ic558fa7bab80b0dabc3e5a06d7494e2688c027b3

unit_tests/__init__.py

@@ -15,6 +15,9 @@
 import os
 import sys
 
+from unittest.mock import patch
+
+
 _path = os.path.dirname(os.path.realpath(__file__))
 _parent = os.path.abspath(os.path.join(_path, '..'))
 
@@ -25,3 +28,15 @@ def _add_path(path):
 
 
 _add_path(_parent)
+
+# 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()