standard testing

#[cfg(test)]
mod tests {

    use super::*;


  #[test]
  fn test_my_function() {
    let result = my_function();
    assert_eq!(result, 42)
  }

How to deal with f64

If you work with floating point numbers f32 or f64 then assert_eq! could fail because of rounding erros.

assertion `left == right` failed
  left: 1.0000000000000002
  right: 1.0

Fortunately there is a crate that helps: approx.

crate add approx

In the root crate of your project (main.rs or lib.rs) you have to insert:

#[macro_use]
extern crate approx;

// using in the test
  #[test]
  fn test_half() {
    let result = half(42.0);
    relativee_eq!(result, 21.0)
  }

More about approx can be found here:

println! during the test

If you print out something during the test you will not see it when running. But there is a flag show the outputs:

cargo test -- --nocapture

or in watch mode and keeping the coloring:

cargo watch -x "test -- --nocapture --color always"

More about display options can be found here:

measure time during test

#[test]
fn test_with_time() {
  let start = ProcessTime::try_now().expect("Getting process time failed");
  // ... do some testing
  let cpu_time: Duration = start.try_elapsed().expect("Getting process time failed");
    println!(" {:?}", cpu_time);
}

Run the tests with

cargo test -- --nocapture

to see the output of the cpu time