Testing yassgy

For this post, I would like to talk about testing yassgy (and how difficult it is...).

I have implement very small test cases on a very small part of yassgy. Since yassgy currently is untestable, and I noticed that refactoring it would a major task, I decided to focus on a really small function of yassgy, testing whether a file path refers to a text file.

I used the built-in testing features included in cargo, by using the cfg attribute and prefixing my test functions with the test attribute.

For example, let us say we have a file called complex.rs, that defines a structure for a complex number:

#[derive(Debug, Eq)]
struct Complex {
  real: f64,
  imaginary: f64
}

impl Complex {
  fn add(self, rhs: Complex) -> Complex {
    Complex {
      real: self.real + rhs.real,
      imaginary: self.imaginary + rhs.imaginary,
    }
  }
}

impl Add for Complex {
  type Output = Self;

  fn add(self, other: Self) -> Self {
    self.add(other)
  }
}

If I wanted to test this structure, I can simply write the following in the same file:

struct Complex {
} 

// snip

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  fn add_two_complex_numbers() {
    let a = Complex { real: 1.0, imaginary: 1.0 };
    let b = Complex { real: 1.5, imaginary: 2.3 };
    let expected = Complex { real: 2.5, imaginary: 3.3 };
    assert_eq!(a + b, expected);
  }
}

And thus, we have implemented the first test case!
This test case can be easily run in the command line with cargo test.

We can also implement a second test case, where we test the subtraction of two complex numbers, and, because we are not supporting a Sub operation, the test case would fail!

Test cases for yassgy

The test cases for yassgy were pretty simple, focused on the function that tests whether a file path refers to a text file.

Writing a few test cases helped me to realize test cases define a specification of your program, and they count in some way as documentation of your program. Thus, testing provide several benefits that outweigh the maintenance costs of the code.