Approval Testing vs TDD

A discussion between two developers on whether approval testing can be considered a form of TDD. One argues that approval tests can drive a TDD-like feedback cycle — writing tests without predefined assertions, then iterating on output until it looks correct — while the other contends this skips a key TDD principle: defining expected behavior upfront. The disagreement centers on whether approval testing's output-driven approach is equivalent to classic TDD's test-first design discipline, or whether experienced practitioners are simply leveraging internalized design skills that TDD originally taught them.