That was exactly it. Thank you!

Probably how your function is handling a negative number as input.

I have attempted to submit but get a failure on the 4th test: '' should equal None. I though this might be saying that an empty string for n (i.e. an invalid input) should return None but I got that working and it tested just fine. Could anyone offer insight into what that failure might indicate that they are testing against?

You might want to avoid comparing Strings with ==, as it can fail under some situations.
Try using string1.equals(string2) instead which is very reliable.

Can someone explain what the square brackets mean in the test cases?

expected:< *

[] *

but was:< *

[***
] *

I'm not sure why my square brackets have three stars in them, but the example doesn't. Also very confused as to where these brackets are comine from. Any assistance would be greatly appreciated!

So to answer @warkentien2's question, is it considered appropriate to use stackoverflow or google to help solve katas? IE, I don't copy and paste the solution from somewhere else, but I use the web to find methods, check syntax, check libraries, etc.