tests/ui/env-macro/option_env-not-defined.rs - third_party/github.com/rust-lang/rust - Git at Google

 //@ run-pass

 pub fn main() {
     assert!(option_env!("__HOPEFULLY_DOESNT_EXIST__").is_none());
 }
	//@ run-pass

	pub fn main() {
	assert!(option_env!("__HOPEFULLY_DOESNT_EXIST__").is_none());
	}