tdd is an indication of how OP's code was written - unit tests first. By itself alongside a language tag, it doesn't bring anything to the table IMO.
unit-testing on the other hand, tells us that OP has unit tests, at least as part of the reviewable code - regardless of whether the code was written with TDD or not.
Since the code is already written, working and tested, whether it was done TDD, OOP and DRY is irrelevant, especially if the unit tests aren't included in the OP.
- a post tagged with tdd without unit tests has an irrelevant tag
- a post tagged with unit tests without a unit-testing tag is missing a relevant tag
- a post tagged unit-testing contains reviewable unit tests
- a post tagged tddunit-testing is a tautology