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: Ice2a2d2379349c8cf7d77027cbca78b19e9d72d1
func-test-pr: openstack-charmers/zaza-openstack-tests#1170

tox.ini

@@ -23,9 +23,9 @@ skip_missing_interpreters = False
 #   lead to fetching the latest pip in the func* tox targets, see
 #   https://stackoverflow.com/a/38133283
 requires =
-  pip < 20.3
-  virtualenv < 20.0
-  setuptools < 50.0.0
+  pip
+  virtualenv
+  setuptools
 
 # NOTE: https://wiki.canonical.com/engineering/OpenStack/InstallLatestToxOnOsci
 minversion = 3.18.0
@@ -34,13 +34,16 @@ minversion = 3.18.0
 setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
          CHARM_DIR={envdir}
-install_command =
-  {toxinidir}/pip.sh install {opts} {packages}
 commands = stestr run --slowest {posargs}
 allowlist_externals =
     charmcraft
-    rename.sh
-passenv = HOME TERM CS_* OS_* TEST_*
+    {toxinidir}/rename.sh
+passenv =
+    HOME
+    TERM
+    CS_*
+    OS_*
+    TEST_*
 deps = -r{toxinidir}/test-requirements.txt
 
 [testenv:build]
@@ -50,30 +53,35 @@ commands =
     charmcraft clean
     charmcraft -v pack
     {toxinidir}/rename.sh
+    charmcraft clean
 
 [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
-       git+https://github.com/juju/charm-tools.git
+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

@@ -13,5 +13,21 @@
 # limitations under the License.
 
 import sys
+from unittest.mock import patch
+
+
 sys.path.append('hooks')
 sys.path.append('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()