Rust for C-Programmers

24.5 Tests That Should Panic

24.5.1 #[should_panic]

You can mark a test that is expected to panic:

#[test]
#[should_panic]
fn test_for_panic() {
    panic!("This function always panics");
}

This test passes if the function panics.

24.5.2 The expected Parameter

You can also ensure that a panic message contains a specific substring:

#[test]
#[should_panic(expected = "division by zero")]
fn test_divide_by_zero() {
    let _ = 1 / 0; // "attempt to divide by zero"
}

If the panic message does not match "division by zero", the test fails. This helps verify that your code panics for the correct reason.