As I mentioned the part in this kata that encourages you to write your own tests is good. I agree with that. But still I wrote my tests and everything was ok. But then when I tried to attempt the solution it gave me errors and the message was that It could not recognise the Ghost class even though I imported the class and passed the tests. And by the way I was using Java to solve the problem.

For SQL, the instructions need to be more clear for a beginner kata. I only managed to pass this by just "assuming" the result only wanted one column after providing 3 and failing the test.

One reasonable solution for Python could be to use typing to give type hints in initial code.

Usually it depends on an initial language used by kat author. If it was Java, C#, JS, etc., they most probably say "array". If it was Python, Haskell, and such, they will say "list". But usually what they mean is an abstract "iterable sequence" and not a specific type of a container. But I can see how this can be sometimes confusing, the OP is not the first person here.

Unless the initial code of the question indicates so, don't take the words "array," "list," and "set" too literally. They're usually used to colloquially refer to an array most of the time (or a dynamic array, depending on the question/language). Since every language calls an "array" by something different, trying to include every possible name is tedious, so a lot of Kata just stick with saying "array" or "list".