For me(I cannot speak for others), it is a judgement that I make on each individual and the task they are undertaken. I can't honestly say my judgement is always correct though! I personally feel some times it is safer that the OP gets some advice that helps them one way or the other.
As I've said, I think many/most of us adopt that approach as best as we can - but, as I've said, in practice, that judgement is really limited to identifying those situations in which an OP is clearly 'out of their depth' (aka 'not competent') in relation to actually undertaking the work, in which case the only appropriate advice is that they should not attempt it.
In relation to testing, the reality is that, no matter what we may convince ourselves, we almost never have any useful information on which to base a judgement. On the contrary, I think we all know that, even if we advise someone about the 'required' tests, the probability of them undertaking them all is extremely small. I would struggle to think of an occasion (at least, in relation to 'minor works') on which, having been told what testing was required, an OP has said that they would go out and hire the equipment, learn how to use it and then undertake all the necessary tests (and, even if they did say that, we couldn't be certain that they were telling the truth).
Hence, if we simply assumed that (even with advice about testing) OPs would never undertake all the required tests, we would only occasionally be wrong, at least in relation to 'minor work'. If we were sticking to our principles, we would/should therefore conclude that the only sensible/safe approach would be to not give anyone any advice/instructions as to how to actually do the work.
However, none of us actually do that. Even you (as well as many others of us) will often give advice as to how something could/should be done, with a comment about the necessary testing merely added 'to the end of that advice' - even though we actually know that the probability of any testing being undertaken is very low.
I personally think that it probably works out about as well as it could, in our imperfect world. However, I don't think that any of us should fool ourselves (or, rather, our consciences) into believing that we are only giving advice (about how to do jobs) to those who are adequately competent and who are going to undertake 'adequate' testing. Speaking for myself, I fully accept that I sometimes give advice to people with very limited understanding (hence probably limited 'competence') and who almost certainly will not undertake any testing - but, in such situations, I give my advice on the pragmatic basis that I believe it better to give them what advice we can, rather than leaving them to muddle along with no advice at all. In other words, I feel to to give the advice is, in that situation, the 'lesser of the evils' in terms of the chances of the OP's safety. BAS, for one, strongly disagrees with that approach.
Kind Regards, John