  We propose a generic test for models in which gravity is modified to do away
with dark matter. These models tend to have gravitons couple to a different
metric than ordinary matter. A strong test of such models comes from comparing
the arrival time of the gravitational wave pulse from a cosmological event such
as a supernova with the arrival times of the associated pulses of neutrinos and
photons. For SN 1987a we show that the gravity wave would have arrived 5.3 days
after the neutrino pulse.
