The dress rehearsal that had to turn back

Two months before the landing, a crew flew a lunar module to within about 15 kilometres of the surface and then climbed away again, which was the whole point.

Apollo 10 was a full rehearsal minus the last fifteen kilometres. The ascent stage tumbled briefly during separation after a switch was set wrong, which is where Cernan's much-quoted swearing on the air comes from, and it is the closest anyone came to the Moon without landing on it.