The following is our very first unit test:

// first_unit_test.rs

#[test] 
fn basic_test() { 
    assert!(true);
}

A unit test is written as a function and is marked with a #[test] attribute. There's nothing complex in the preceding basic_test function. We have a basic assert! call passing in true. For better organization, you may also create a child module called tests (by convention) and put all related test code inside it.