Compiling any code[1][3] with the --test flag spits out a warning[2][4] on the first token it finds. [1] test.rs ``` extern mod std; pure fn bigger_than(x: int, y: int) -> bool { return x > y } #[test] fn t1() { assert bigger_than(5, 3) == true; } #[test] #[should_fail] fn t2() { assert bigger_than(3, 5) == true; } ``` [2] rustc output ``` λ rustc --test test.rs test.rs:1:0: 1:0 warning: argument 1 uses an explicit mode test.rs:1 extern mod std; ^ ``` [3] test2.rs ``` // extern mod std; ``` [4] rustc output ``` λ rustc --test test2.rs test2.rs:1:0: 1:0 warning: argument 1 uses an explicit mode test2.rs:1 // ^ ```