Well, yeah!
Looking into this a little bit, I found that a proposed J-2T was designed with an aerospike nozzle, which obviously means that it was designed for use with atmospheric pressure. The J-2X has no need of that, so a test stand built specifically for sea-level conditions is useless. I wonder if this test stand is being built just in case they decide to revive the J-2T program, but using the fuzzy justification of the J-2X requirements for the Ares program. I suppose a rocket built with just J-2Ts and J-2Xs would be pretty cheap for space probes and such.