[stable-2.13] ansible-test - Adjust unit test mock usage. (#77961) (#77999)

(cherry picked from commit 23914d3f0b)

Co-authored-by: Matt Clay <matt@mystile.com>

changelogs/fragments/ansible-test-ansible-core-mock.yml

@@ -1,3 +1,2 @@
 minor_changes:
-  - ansible-test - Avoid using the ``mock_use_standalone_module`` setting for ``pytest`` when running ansible-core unit tests.
-                   This has no effect on unit tests for collections.
+  - ansible-test - Avoid using the ``mock_use_standalone_module`` setting for unit tests running on Python 3.8 or later.

test/lib/ansible_test/_data/pytest/config/ansible-core.ini

@@ -1,4 +0,0 @@
-[pytest]
-xfail_strict = true
-# avoid using 'mock_use_standalone_module = true' so package maintainers can avoid packaging 'mock'
-junit_family = xunit1

test/lib/ansible_test/_data/pytest/config/default.ini

@@ -1,4 +1,4 @@
 [pytest]
 xfail_strict = true
-mock_use_standalone_module = true
+# avoid using 'mock_use_standalone_module = true' so package maintainers can avoid packaging 'mock'
 junit_family = xunit1

test/lib/ansible_test/_data/pytest/config/legacy.ini

@@ -0,0 +1,4 @@
+[pytest]
+xfail_strict = true
+mock_use_standalone_module = true
+junit_family = xunit1

test/lib/ansible_test/_internal/commands/units/__init__.py

@@ -21,6 +21,7 @@ from ...util import (
     ANSIBLE_TEST_DATA_ROOT,
     display,
     is_subdir,
+    str_to_version,
     SubprocessError,
     ANSIBLE_LIB_ROOT,
     ANSIBLE_TEST_TARGET_ROOT,
@@ -234,12 +235,21 @@ def command_units(args):  # type: (UnitsConfig) -> None
     if args.requirements_mode == 'only':
         sys.exit()
 
-    if data_context().content.is_ansible:
-        config_name = 'ansible-core.ini'
-    else:
-        config_name = 'default.ini'
-
     for test_context, python, paths, env in test_sets:
+        # When using pytest-mock, make sure that features introduced in Python 3.8 are available to older Python versions.
+        # This is done by enabling the mock_use_standalone_module feature, which forces use of mock even when unittest.mock is available.
+        # Later Python versions have not introduced additional unittest.mock features, so use of mock is not needed as of Python 3.8.
+        # If future Python versions introduce new unittest.mock features, they will not be available to older Python versions.
+        # Having the cutoff at Python 3.8 also eases packaging of ansible-core since no supported controller version requires the use of mock.
+        #
+        # NOTE: This only affects use of pytest-mock.
+        #       Collection unit tests may directly import mock, which will be provided by ansible-test when it installs requirements using pip.
+        #       Although mock is available for ansible-core unit tests, they should import units.compat.mock instead.
+        if str_to_version(python.version) < (3, 8):
+            config_name = 'legacy.ini'
+        else:
+            config_name = 'default.ini'
+
         cmd = [
             'pytest',
             '--forked',