One prediction was the time-dialation predicted by special relativity. This was confirmed when an experiment was made whereby two airplanes few in opposite directions (one west, and one east) and the time shown by the synchronized clocks differed by a small amount.
Another prediction was the bending of light by gravity (gravitational lensing), this was famously confirmed by the observation of distant stars and galaxies during a solar eclipse (the image showed those galaxies to be somewhere slightly different from where they were predicted to be, due to the curving of light around the Sun).