Don't really see much point of testing the fuel striaght after refueling the whole lot is going to be mixed up so for it to be any good you will need it to sit for awhile to settle.
Believe me, it doesn't take long to settle (5 minutes isn't going to cause you any problems - if you're in that much of a rush should you really be flying?) and it proved itself to me at Le Touquet one day with 3 1/2 strainers full of crap.