One of my Facebook friends recently posted a link to this song, which was a favorite of mine during my law school days (especially when studying evidence). The Parliaments were a group founded by George Clinton in the late 1950s, inspired by Frankie Lymon and the Teenagers. The band stayed together (although probably with some personnel changes) without a hit until "Testify" made the charts in 1967.
In the 1970s, the Parliaments evolved into Parliament which, along with another Clinton-led group, Funkadelic (referred to collectively as Parliament-Funkadelic), did music in a style called "P-Funk". In 1974, Parliament re-recorded "Testify" with a P-Funk groove. (Thanks to Xpinger for the 1967 "Testify" clip, and to BigMTown2 for the 1974 version.)