NOOOOOOO...read it again!! You have to have an endorsement from an instructor on those subjects...but not to take the knowledge test.
See, if you look in 61.123, in the section that deals with the commercial, Section (c) (2), a CFI in that case muct certify that you are prepared to take the test.
For the CFI, however, you don't need an endorsement to take the test. But you will need an instructor to endorse that you have recieved that knowledge before you can be ELIGIBLE to be a CFI.
Make sense now?