Has Anybody Seen My Gal (1952)

Wealthy Samuel Fulton is getting older and has no family of his own. He decides to leave his estate to the family of his first love, who turned down his marriage proposal years ago because he was poor. But he wants to test the family before leaving his money to them. He takes a room in their home and a job in the father's shop. He anonymously grants them $100,000. Harriet Blaisdell moves the family into a mansion and makes plans to marry her daughter Millicent off to a socialite rather than her soda jerk boyfriend Dan. The money goes to their heads, and they soon find themselves broke, back in their old house, and back to their old lives. Father back in his shop, Millicent engaged to Dan, and everyone seemingly much happier. Hoping they learned their lesson, Fulton takes his leave of the family.