my question... if the in-season testing is 'strictly' banned then how come teams develop new parts and put it on the car??... does that mean the parts are developed without testing (somewhat blindly) and they 're put on the car on the very race weekend? :S ...
and if so then how come ferrari knew in advance that their 'big upgrades' will work in valencia??.. oh right.. they tested them on 'filming day' ...
Developing new parts have nothing to do with in-season testing until they are designed and developed, testing only needed to verify what they assume whether they have achieve that or not. Big teams have super computers on which they do simulations runs of new equipments, also windtunnels testing is allowed for a limited no. of hours for the full season.
In-season testing ban is only for track testing, where new parts are integrated on the car, although straight line testing is allowed for a limited days.
Ferrari's assumption for what kind of performance gain they get from the blown diffuser and new rear wing was based on simulation and has nothing to do with the "filming day testing", yes they have violated the gentlemen's agreement between the teams but it was not that serious to consider a big thing.
The same is for RedBull's new wing situation, what ever they assume to gain from new wing was either not gain or they never intended to use it for this circuit, but may be that wing could give some substantial advantage on Hockenheim.