chore: add TODO for tests

Co-authored-by: Kyle McCormick <kyle@kylemccormick.me>

Author: NiedielnitsevIvan

tests/openedx_learning/apps/authoring/subsections/test_api.py

@@ -16,6 +16,9 @@
 Entry = authoring_api.SubsectionListEntry
 
 
+# TODO: Turn UnitTestCase into UnitTestMixin and remove the
+# test-inherits-tests pylint warning below.
+# https://github.com/openedx/openedx-learning/issues/308
 @ddt.ddt
 class SubSectionTestCase(UnitTestCase):  # pylint: disable=test-inherits-tests
     """ Test cases for Subsections (containers of units) """