It's generally considered as bad practice to mutate the input.

The tests are OK but you should not modify the input list ls; work on a copy of ls. Moreover there might be some other problems in your code.

There is nothing messed up in the tests: look at the top of the page to see how many people passed the Python kata.

Bigger numbers: 880 8 [] --> first the list of distances is empty

Print the list and you will see it is not empty.