django.db.models.query_utils.RegisterLookupMixin._unregister_lookup method also should clear the cache stored for django.db.models.query_utils.RegisterLookupMixin.get_lookups

[Himanshu Balasamanta]

Hi Carlton.
I have opened the PR ​https://github.com/django/django/pull/15569, and have also modified the test that was supposed to throw error(schema.tests.SchemaTests.test_func_unique_constraint_lookups).

There is no test that checks if the lookup stays in cache after unregistering it. In my PR, I have added an assert statement to check it in custom_lookups.tests.LookupTests.test_lookups_caching test. Running the test without clearing cache from _unregister_lookup will fail.

The cache stays between tests, so you are likely to get different results running tests independently and running all tests in a module. (PS: I faced this problem earlier running tests individually and together gave different results.)

[Carlton Gibson]

Hi Himanshu. This may be right, yes — I need to have a sit-down and play with it.

Main question: Are you able to put together an example case where the wrong result arrises?

• I was looking at ​PR #6906 which added the cache clearing.
• Also noting the For use in tests only... in the _unregister_lookup docstring. So this would show up in a test inter-dependency...? 🤔