Updated test constraints for mock assert_called() and assert_called_once()

test/runner/requirements/constraints.txt

@@ -21,6 +21,8 @@ virtualenv < 16.0.0 ; python_version < '2.7' # virtualenv 16.0.0 and later requi
 pyopenssl < 18.0.0 ; python_version < '2.7' # pyOpenSSL 18.0.0 and later require python 2.7 or later
 pyfmg == 0.6.1 # newer versions do not pass current unit tests
 pycparser < 2.19 ; python_version < '2.7' # pycparser 2.19 and later require python 2.7 or later
+mock >= 2.0.0 # needed for features backported from Python 3.6 unittest.mock (assert_called, assert_called_once...)
+pytest-mock >= 1.4.0 # needed for mock_use_standalone_module pytest option
 
 # freeze pylint and its requirements for consistent test results
 astroid == 2.0.4

tox.ini

@@ -22,6 +22,7 @@ passenv =
 [pytest]
 xfail_strict = true
 cache_dir = .pytest_cache
+mock_use_standalone_module = true
 
 [flake8]
 # These are things that the devs don't agree make the code more readable