The shut down has always been an optional item under JAR-FCL however there is no guidance on what "optional" means.
In the old UK M/E Skill Test an engine shut down was mandatory, now it is not. An examiner may at his discretion ask a candidate to perform any manoeuvre taught on the training course for which he is testing. The skill test is the means of determining if the aim of the course has been met; it does this by sampling major items, rather than testing everything 100%. Usually, additional (optional) items are only added to satisfy the examiner that a candidate is a pass or a fail i.e. it is to clarify some doubt in the examiners mind. There is no call to conduct optional items just because the examiner feels like it; the test should normally be confined to the published Mandatory items.
I agree with Chuck there is no point in closing down a serviceable engine. If you have never seen it, there is some value, though others might dissagree. You should not be asked to do it on each renewal.
If you do not agree with the examiner you have a right of appeal under CAA Regulation 6, regarding the conduct of the test. If you are asked to perform an optional item, the examiner must be prepared to explain the reason.