examples

Test-driven development - example

For this test-driven development example, imagine you want to write a function foo that always returns true.

First write a test:

#[cfg(test)]           // Annotation: the mod is for cargo test
mod tests {            // Define a module named "tests"
    use super::*;      // Use code from the outer module

    #[test]            // Annotation: this function is a test
    fn foo_test() {    // Define a function as usual
      assert!(foo());  // The assert! test macro must be true
    }

}

Verify the test failure:

cargo test

Write the simplest code possible to pass the test:

pub fn foo() -> bool { // Define a function
    true // Always return true
}

Verify the test success:

cargo test

Rust has built-in test assertion macros such as assert, assert_eq, assert_ne. In practice, these are fine for simple TDD, but may be too basic for real-world TDD. In our real-world projects, we use the Assertables crate that provides many more assertions such as assert_starts_with, assert_contains, and assert_is_match.

https://crates.io/crates/assertables