I think maybe it's saying that your cipher function returned 'eta' and the test was expecting 'qxz'. There aren't any problems with the test cases, but maybe the message should be more clear (in which case, you could write to Codewars saying their assertEquals output on test failure is confusing).

Test Passed
'eta' should equal 'qxz'
i think there is some problem with test cases.

My code works fine and outputs: 335045203092460 (for the underneath inputs) but it is giving me the following error in submission. Please resolve the issue with Kata.
f(25886104, 85766697)
Traceback:
in
in f
TypeError: integer argument expected, got float

I can understand that the output is large, but there is not information given for rounding off etc.