"The Game of Love and Chance" by Marivaux. Apparently he was pretty well known in the 18th C., but he's a bit more obscure now, I guess.
A young woman learns that her father has arranged a marriage for her, and she is to meet her intended soon to see if they like each other. She swaps places with her maid, so she can observe him secretly when he's not trying to impress anyone. The young man arrives, having swapped places with his valet for the same reason. Mistaken identity-type romantic comedy ensues.
It was a fun play, if a littly chaotic around the edges.