The hint to use get() method for looking up the value of the token in sys_coynter and ref_counter dictionaries resulted in the unit tests failing (1 pass, 3 failed).
But instead using sys_counter[token] and ref_counter[token] made all unit tests pass! Weird!!
The Python dictionary .get() method returns the value of the item with the specified key and if you optionally specify “no_key_value” that will be returned.
So you should use it the right way, for example: sys_counter.get(token, 0)
and the test will not fail.