Similarly, there's the the TV series Noisnecsa (reverse the letters) where it starts out with the premise that they've going through space on such an inter-generational voyage, in a massive, self-sustaining ship. Then later there's a reveal that it's just experimental and stayed on the ground the whole time, with mission control monitoring them and periodically communicating.

(It was described as a hybrid of Mad Men and Battlestar Galactica.)