Getting asserting the value None error when unit testing with Pytest
I believe that this error occurs because of the function pandas.testing.assert_frame_equal returns None if frames are equal; if they're unequal it raises AssertionError. Therefore you're actually checking assert None.
So I think you should remove assert operator here and just write
testing.assert_frame_equal(expected, result)Or write
assert testing.assert_frame_equal(expected, result) is None