Simulating observations to test general relativity in its strongest regime at the Galactic Center with the instrument GRAVITY.

Probing gravity in the immediate vicinity of a supermassive black hole would be a powerful test of general relativity (GR). The Galactic Center is an ideal laboratory to do so. Indeed, flares are regularly observed there, which could be due to a hot spot orbiting on the last stable orbit of the black hole: a perfect probe of strong gravity.
The precise observation of such events will be possible in the near future thanks to the second generation VLTI beam combiner GRAVITY. To determine the level at which this instrument will put constraint on general relativity, a full GR ray-tracing code has been developed: GYOTO. The aim of this talk is to present recent results from this code. I will insist on the simulation of a hot spot orbiting either around a Kerr black hole, or an alternative compact object.
These results are in turn used as inputs to a code simulating the instrument GRAVITY. The final objective is to determine to what extent GRAVITY will allow to constrain the nature of the central compact object and to probe space-time in its surroundings.