  The capture of a stellar-mass compact object by a supermassive black hole and
the subsequent inspiral (driven by gravitational radiation emission) constitute
one of the most important sources of gravitational waves for space-based
observatories like eLISA/NGO. In this article we describe their potential as
high-precision tools that can be used to perform tests of the geometry of black
holes and also of the strong field regime of gravity.
