Once it has a reply, no, you can't, don't worry.

I was just coming back to delete my comment (guess I can't?), the problem is mine. I mixed the expected and actual values.

Which language are you talking about? If it is Python the tests are fine:

It should work for random inputs too: None should equal '-100,-97,-96,-94,-93,-90,-87,-85,-82,-80--75,-72,-69,-67'

I don't see as you claim, -97--96 or -94--93 in the expected result.

It should work for random inputs too: 
'-78,-77,-75,-73,-71--69,-66,-65,-62,-59--57,-54,-53,-51--50' # your answer
should equal
'-78,-77,-75,-73,-71--69,-66,-65,-62,-59--57,-54,-53,-51,-50' # expected value

Your code is producing the wrong answer there, it's the first one in the error message.

For ranges of only 2 consecutive numbers, for example [2, 3] in [0, 2, 3, 5], the tests expect it to be shown as individual numbers '2,3' if the numbers are positive, but as a range '-3--2' if the numbers are negative. Shouldn't it be consistent for negative and positive numbers?

Yes, this is very clever!

Is that a compliment?

You cheeky bastards.