In addition to the standard operational refueling missions that are part of normal station-keeping operations, there have also been experiments performed that studied in-space refueling.
In particular, three phases of the NASA Robotic Refueling Mission have been completed, which simulated on-orbit refueling of a satellite not designed for refueling. A module was installed on the outside of the ISS that mimicked the fueling connections on a typical satellite. Note that "fueling connections on a typical satellite" here means the kinds of connections, valves, seals, etc. that you would find on a satellite not designed for refueling, to be only used once, on the ground, for initial fueling of the satellite.
Using these connections that were never intended to be re-used and never intended to be used in-flight, the RRM successfully demonstrated on-orbit refueling of hypergolics, oxidizer, and cryogenics.