This is an interesting test.
Would it make sense to test the original qualname first, then assign a different one and test that PyType_GetQualName returns the replacement?

Haha. I try to get some qual names in _testcapimodule. But I can get the qual name with prefix.
The reason is res->ht_qualname = res->ht_name; in https://github.com/python/cpython/blob/main/Objects/typeobject.c#L3439.
I don't know the reason why the qual name need to reomve the prefix too.
So I set a qual name with prefix to test this C API, somthing like a mock behavior~

Right, C-API classes don't have distinct qualnames.
IMO, the best thing to do here would be:

• Test the original qualname (same as the short name)
• Change the qualname
• Then test the new qualname.

Ideally, the same thing would be tested for PyType_GetName as well – it's not that different from this function.

Right, C-API classes don't have distinct qualnames.
IMO, the best thing to do here would be:

• Test the original qualname (same as the short name)
• Change the qualname
• Then test the new qualname.

Make sense. How about this updated PR :)

Ideally, the same thing would be tested for PyType_GetName as well – it's not that different from this function.

Got it. I will update enhance this test case later.