Check my recursive solution if interested. Similar approach but I needed extra method (to be able to pass list as parameter).

You are right.
Broken codes which raise exception didn't fail tests before.
This is due to a bug in exception handling.
This bug has been fixed now, which results in the Test cases to run as intented.
Thank you for pointing out!

Maybe I'm missing something, but I don't think this solution is valid. It throws an ArgumentNullException on AddRange if the rectangle becomes a square.

I believe arraysSimilar([1,2], [0,3]) should return false. There are some solutions that pass the other tests, but not this one.

The above code is still incorrectly accepted. The following test case should reject the above answer:

Test.expect(!validPhoneNumber("a(123) 456-78900"));