the test is probably a bit paranoid. It iterates several thousand times.
it tests many alignments, aliasing permutations, and with a nan in every position. It needs to do this because it needs to handle nan in the peeling loop, nan in the cleanup loop, nan in first operand of the vector register, nan in second, etc.
Now that we know the approach taken works one could relax the test or move it to slow tests, or as done here, make it faster :)