tests/ui/fmt/ifmt-unknown-trait.rs - rust-lang/rust - Git at Google

 fn main() {
     format!("{:notimplemented}", "3");
     //~^ ERROR: unknown format trait `notimplemented`
 }
	fn main() {
	format!("{:notimplemented}", "3");
	//~^ ERROR: unknown format trait `notimplemented`
	}