Fix a flaky test by cleaning a polluted state.

[sturmianseq]

What is the purpose of the change

This PR is to fix a flaky test cynergy/tests/test_register_multiple.py::test_register_multiple, which can fail after running cynergy/tests/test_register_multiple.py::test_multiple_list_arguments_with_wrap, but passes when it is run in isolation.

Reproduce the test failure

Run the following command:

python -m pytest cynergy/tests/test_register_multiple.py::test_multiple_list_arguments_with_wrap cynergy/tests/test_register_multiple.py::test_register_multiple

Expected result

Test cynergy/tests/test_register_multiple.py::test_register_multiple should pass when it is run after test cynergy/tests/test_register_multiple.py::test_multiple_list_arguments_with_wrap

Actual result

Test cynergy/tests/test_register_multiple.py::test_register_multiple fails:

E       AssertionError: assert <class 'cynergy.tests.test_register_multiple.Example2'> is Example1
E        +  where <class 'cynergy.tests.test_register_multiple.Example2'> = type(<cynergy.tests.test_register_multiple.Example2 object at 0x7f6699140eb0>)

Why it fails:

After running cynergy/tests/test_register_multiple.py::test_multiple_list_arguments_with_wrap, the container is polluted.

Fix:

Clear container each time before cynergy/tests/test_register_multiple.py::test_register_multiple runs.