A 170a is a UK thing which dates back to when all IR's and a lot of CPL's were tested by CAA employed examiner.
There was a set of examiners who weren't employed by the CAA who were authorised to pre test the candidate which they had to pass before getting sent on to the CAA ones. It was I think a way of only making likely passes going for the full thing.
Unfortunately it was perverted by some schools as a method of extracting more money from the student.
There was never a requirement for a flight test for the CPL only a paperwork check but many schools still demand a flight test outside the CPL course.
For the IR there is a bit of a grey area now as its not compulsory for you to use a CAA examiner. The test is normally done but there have been some who have managed to by pass the test and go straight to test because under EASA and JAR I believe there is no requirement for it. Obviously the schools don't like this as its 2.5 hours in the aircraft and also the local examiner also gets a fee for the test. In a twin including approach fees this can cost over £1000 per test.
At the beginning of JAR there was a bit of confusion about how it was all applied. And quite a few of us managed to get the 170a included in the course and also that the full time in the aircraft from taxing to stop was included in the course hours. Which personally saved me about 5 hours on the course of 55hours and a 2.5 hour test and approach fees. So about 2.5k at the prices at the time. The UK CAA won't allow this now.