Some tests, such as for the PPL, require an instructor's endorsement. Others, such as for the CFI, do not. Is there any logic behind this, or is this just an artifact of the merge of two historically separate test approaches?
The CFI written exam includes 100 questions of a pool about a 1,000 and most of the questions are common to the Private and Commercial Pilot written exams. If you already passed those there isn't a lot of reason to require an instructor to sign you off to take the CFI test.