You're testing recall only when asking about TLS. You may be testing recall for "how to implement a known algorithm", but there's still plenty of room for testing actual problem solving too.
If you are the interviewer, even if you are asking a standard "how to invert a binary tree" type algorithm question, you hold the cards to keep pushing the bounds for problem solving by extending the question.
If you are the interviewer, even if you are asking a standard "how to invert a binary tree" type algorithm question, you hold the cards to keep pushing the bounds for problem solving by extending the question.