[eaq]

I'm not so surprised that there are no GR deviations in these early days of detections that are just becoming significant over the instrument noise.

GW physicists are hard at work on the future generations of GW detectors... In 50 years, a signal like GW150914 might have an SNR of >1000, so we'll see all kinds of detail that may hold more information than what we've seen so far.

[ISL]

People have been testing GR really hard for a century, especially in the last fifty years. Nobody's convincingly found a single chink in the armor.

Clifford Will's "The Confrontation between General Relativity and Experiment" is an excellent introduction to the state of the art (this is the stock reference for everyone in the field).

http://relativity.livingreviews.org/Articles/lrr-2014-4/