Boston Beanie (1947)

A homeless cat singing, "Hallelujah! I'm a bum" encounters the home of a Mister Lavish McTavish who adopts the cat and promises him all the food he can eat... but ONLY if the cat proves his worth by capturing the mice loose in his house. As it turns out, there is only one mouse in the house who makes a deal with the cat to save his skin.