Some URLs like www.google.com are used very often, it can happen that two users want to shorten the same URL, so you have to check if this URL has been shortened before to save memory in your database.

Your code isn't handling duplicates correctly.

Just go for 'Attempt'.

Still not possible...

Because apparently you are not the only one who decided to use regex and forgot about the fact that you cannot just use an arbitrary string as a part of regular expression, but also did not test their solution sufficiently locally ;)

Print the inputs, recreate failing tests locally, and observe them failing.

No, it seems there's no issue with tests.