Apollo 10 was the second manned test in orbit around the Moon. The test took place in May 1969. The flight tested the Lunar Module in Moon orbit.
The Lunar Module separated from the Command Module, and descended to about 9 miles above the surface of the Moon. At this height a rescue could still be performed by the Apollo Command Module.
There were problems with the Lunar Module separating from it's landing stage when it was ready to re-ascend to join the Command Module.