There's a disconnect between TDD using all sorts of tests (unit, integration, hardware-in-the-loop, in-field, etc.) and TDD using unit tests only. Unit tests provide the least value/line of test code of all types of tests. They're important, since they can catch bugs earlier than other sorts of tests that can't be caught by a type system, but not sufficient to catch most bugs.

It is however how most software testing is done.