Let's look at it from a different perspective then - the online slaggers and gossips were speculating very early on that the children had been sedated by their parents, so as a concept the sedation of the children was a very hot topic at the time. The PJ suspected the parents, knew they left them unattended, believed Madeleine had died somehow and her death covered up by her parents - why wouldn't they have considered misuse of drugs as a possible factor in the case? Were the PJ not as clever at thinking outside of the box as the armchair detectives?
I think the key phrase is "online slaggers and gossips". If you are correct in this respect, I am aware of many a scurrilous rumour that appears to have surfaced in this manner, none of which has, AFAIK, entered the PJ Files.
I don't believe the PJ sat around thinking up hoops they could make the McCanns jump through, at least not until the doggies and the FSS seemed to provide a line of enquiry to be pursued.
I am not sure what the process was for getting the twins tested 1) when the Lisbon CSI team tested for and found no anaesthetics and 2) the nearest thing to 'solid evidence' was a couple of GNR officers stating the twins did not react to being relocated.
Despite what many think or assert, there is ample evidence in the PJ Files to show that legal process was being followed regarding house searches, car searches, obtaining DNA samples, collecting and analysing phone traffic. The PJ did not conduct such processes illegally, though I have seen criticism of them for not house breaking etc.
In the complete absence of evidence that the PJ knew of potential drugging and failed to act, I really can't see why anyone expects them to know that people like us think a test on the twins would be beneficial.