Advanced LIGO and Virgo have already detected black holes crashing into each other ten times. With their upgrades we anticipate a rate of about 1 gravitational-wave detection per week. More signals and higher precision will take the dream of testing Einstein’s theory of gravity, general relativity, and make it a reality. But would we know a correction to Einstein’s theory if we saw it? How do we make predictions from theories beyond GR? And do current numerical relativity simulations have enough precision that we could be confident in any potential discrepancy between observations and predictions?