You can test it without ingesting it. With hundreds of reviews I'd hope a few people were smart enough to sacrifice some of their MDMA to test it.
I guess that it depends on how easy it is to test it. If it requires a chemistry degree and a lab I am guessing they won't test even if they are otherwise smart.
[0]: http://www.dancesafe.org/product/coomplete-adulterant-screen...
Anyways, as someone stated above, these kits test for the presence of MDMA, not necessarily all adulterants. There is the issue of cross-reactivity as well.
It's better than nothing, but I'm not sure I would trust a drug that hadn't been run through an HPLC.