Doctest doesn't check __repr__
equality, per se, it just checks that the output is exactly the same. You have to ensure that whatever is printed will be the same for the same dictionary. You can do that with this one-liner:
>>> sorted(my_function().items())
[('a', 'dictionary'), ('this', 'is')]
Although this variation on your solution might be cleaner:
>>> my_function() == {'this': 'is', 'a': 'dictionary'}
True