I didn't get to finding the exact cause of your problems, but I noticed that your solution seems to work when called once, but fails when called twice. Notice how following test cases:

test.assert_equals(fib(96), 51680708854858323072)
test.assert_equals(fib(-96),-51680708854858323072)

pass when run separately, but the second one fails when both tests are run in one go. I am too noobish with Pytohn to pinpoint the issue, but I know that default parameters in Python can cause some surprises sometimes because they retain values between tests.

Hope this helps. I am going to mark the issue as resolved, since I believe kata is OK, and problems are caused by some bug in your solution. If you can confirm that the kata is bugged, feel free to re-raise it giving some details.

Intentation is not a mess if you post your code properly.