Could you give more details for reproduce it because on the latest version cpython from master branch it's work
You can debug it with help pdb. Just set breakpoint:

...
test_shelve(data)
breakpoint()
data.close()
...

And try run it step-by-step (press 'S' to go to the next step and press 'll' to know where you are now)
https://docs.python.org/3/library/pdb.html#debugger-commands