The CPython test suite uses a counter on memory allocations. Please add an unit test which triggers the memory leak, but you don't need many iterations. One iteartion should be enough to be catched by the unit test. Try: ./python -m test -R 3:3 test_dict.

The memory allocation counter:
https://docs.python.org/dev/library/sys.html#sys.getallocatedblocks

Note: The tracemalloc module can also be used to track memory leak, but it's harder to use it to write unit tests because Python uses a lot of internal caches and tracemalloc really tracks every single bytes.