How to test a method inside an implementation in Rust [closed] - testing

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I'm trying to increase the test coverage in my Rust application. I have read lots about testing public functions and testing private functions and adding the "tests" directory in order to add integration tests. But I have not read anything about testing of methods within an implementation. I've tried googling a bit for this but I'm not finding anything.
Here is a simple example, is this how I am meant to implement the testing?
struct Rectangle {
width: usize,
length: usize,
}
impl Rectangle {
pub fn new(width: usize, length: usize) -> Rectangle {
Rectangle {
width,
length,
}
}
fn area(&mut self) -> usize {
self.width * self.length
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_rectangle() {
let mut rectangle = Rectangle::new(4, 5);
assert_eq!(20, rectangle.area())
}
}

Answer 1

Yes, that is exactly how you are meant to test struct methods. The Rust book has a chapter called Test Organization which states:
The purpose of unit tests is to test each unit of code in isolation from the rest of the code to quickly pinpoint where code is and isn’t working as expected. You’ll put unit tests in the src directory in each file with the code that they’re testing. The convention is to create a module named tests in each file to contain the test functions and to annotate the module with cfg(test).
Another common test organization methods is using documentation tests. rustdoc supports executing your documentation examples as tests. So running cargo test on the example below would cause the area function to execute as a test:
impl Rectangle {
/// ```rust
/// use crate::Rectangle;
///
/// let mut rectangle = Rectangle::new(4, 5);
/// assert_eq!(20, rectangle.area())
/// ```
fn area(&mut self) -> usize {
self.width * self.length
}
}