We can prefix a function with the #[test] attribute to indicate that it is part of the unit tests for our application or library. We can then compile with rustc --test program.rs. This will replace the main() function with a test runner and show the result from the functions marked with #[test]. Have a look at the following code snippet:
// from Chapter 3/code/attributes_testing.rs
fn main() {
println!("No tests are compiled,compile with rustc --test! ");
}
#[test]
fn arithmetic() {
if 2 + 3 == 5 {
println!("You can calculate!");
}
}Test functions, such as arithmetic() in the example, are black boxes; they have no arguments or returns. When this program is run on the command line, it produces the following output:
However, even if we change the test to if 2 + 3 == 6, the test passes! Try it out. It turns out that test functions always pass when their execution does not cause a crash (called a panic in Rust terminology), and it fails when it does panic. This is why testing...