Since the commit 45700fb757591a672e9d25b8252971c2a2caeaf2, test_genericclass leaks references:
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vstinner@apu$ ./python -m test -R 3:3 test_genericclass -m test.test_genericclass.CAPITest.test_c_class
Run tests sequentially
0:00:00 load avg: 1.27 [1/1] test_genericclass
beginning 6 repetitions
123456
......
test_genericclass leaked [2, 3, 2] memory blocks, sum=7
test_genericclass failed

1 test failed:
    test_genericclass

Total duration: 107 ms
Tests result: FAILURE
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The leak comes from _testcapi.Generic[int]. Maybe from generic_alias_new() of Modules/_testcapi.c.