The task sounds as 'if given object is a digit (0-9)'. 'is a single digit' would make it more clear. Because 0-9 is a typical pattern for regex-related thoughts and it really misleads.

I can pass all the tests but not pass the problem because AssertNull throws an error. Needs to be fixed. Just take out that AssetNull and it will actually match the description which say one can assume you don't have to check for null.

A classic alternative in Python ;-)

I'm finding the errors are popping up frequently with the random tests. My code passed the first time and I decided to simplify it (less readable but shorter). I found that sometimes the random tests would give me what appear to be false negatives. I was wondering if it was my code, but I tried it with other solutions in here and had the same issue.

I assume there is a chance it's something I'm doing, but I suspect it's not because of having tested it with various solutions.

I want to suggest the prompt instructions be written so that they are a little clearer and don't suggest the isdigit solution. For example:

Your function should return True if a function is a single digit (i.e., 0-9) and False otherwise.