i am 99% sure that you dont have to pass an IR flight test
Yes you DO. What you are referring to is the "Foreign Pilot Instrument written test" which is indeed the only test you need to do to add a fooreign IR to the restricted PPL.
However,a foreign instrument rating does NOT carry over to the CPL.
You will the have PPL-IR (restricted) and FAA CPL (VFR only)
For the IR to carry over it needs to be "US test passed".