I pass the test cases. But when I submit I get 'TypeError: Cannot call method 'count' of undefined' and I really don't understand why. Can someone please give me a hint about what I'm doing wrong?

'Did you check for invalid values?'. What does this mean? What invalid values?

I don't know exactly what error are you referring to, but I get an error because random test is (8, 'I') (2, 'C'). I didn't know that there could be a a 8I position in chess. I can pass the test by addding an 'I' to the index, but the python tests are broken.

I had some problems understanding the error handling too.

Errors, if:

n is not a number
n not an integer
n is negative or 0

The three functions should respectively return [], [[],[]] and [].
So the first function should return [], the second one should return [[],[]], and the last [].
I hope this is going to help you.

What should I understand from this: the beginning [-0] the end is valid, but no match was made.: False should equal True? I'm passing some tests, but not this one.