Test. Test. Test away. Just don't test too many in one sitting otherwise your nose tires, I believe, and you may miss something good OR bad.
For me, the best card test is the first, so I go to the fragrance I am most curious about (decisions based on Basenotes info.). I might try "serious" tests for 3 - 4 others (total of 5). While I'm testing one, the other/s are drying down a bit, then I go back to the first, second, etc. to test the dry down. I keep the cards separate and on my person. I may "fun" test other fragrances knowing my nose has probably been pretty corrupted by everything previously, but I don't stash those cards away. If my skin is not clean and neutral smelling I do not skin test. I walk away with the cards and check on them occasionally.
If the winner of the first 1 - 5 is impressive, it gets sprayed on my skin and I walk far away, into the real world, far from any strong odors. I check it often for the rest of the time.
I'll go back 2 - 3 more time for skin tests, before I consider buying. I'll also ask honest friends of good taste and significant others.
Very few fragrances make it through the ordeal as I'm very critical. One bad thing and I won't buy it.