An interactive tests that involves T/R or flying control movement then there should be someone in the flt deck, also some tests can be quite lengthy but don't require any interaction, 60 minutes or more, so could potentially compromise this, having to start again, with a possible delay. I always try to be there, to advise crew please don't touch.... That said it would be courteous to check before moving grnd test enable etc, as we can not always be in 2 places at once. A lot of tests on the 350 for instance require ADIRU alignment, first thing crew do on arrival, start a realignment, so if I know the crew are imminent I will endeavour to tell them, and to be fair a lot of our crews do ask first.