Rust - Testing Code

Rust Testing

Cargo Test

To run single specified test case:

cargo test <test_case_name>

To run only tests from particular test file:

cargo test --test integration_test

Test with logs printed:

cargo test -- --nocapture

Unit Tests

In Rust unit tests may be written alongside to the code under test.

To create test function you need to mark it with #[test] macro:

#[test]
pub fn test_1() {
    // ... test code
}

Also several test cases could be organized into test module with #[cfg(test)]:

#[cfg(test)]
mod tests {
    #[test]
    fn test_1() {
        // ... test code
    }

    #[test]
    fn test_2() {
        // ... test code
    }
}

#[cfg(test)] macro tells Rust compiler to build this module only when cargo test command is executed.

Using test modules like that also allows to test private function, which are external to it. For example: 

fn private_function() {
    // some code
}

mod tests {
    use super::private_function;

    #[test]
    fn test_1() {
        // test private_function here
    }
}

Integration Tests

In Rust concept of integration testing means such kind of tests, which test behavior of our library from position of external user. Integration tests are checking correctness of the public API and all classes and functions working together.

To create integration tests need to create tests directory in the root of the project:

our_crate
├── Cargo.lock
├── Cargo.toml
├── src
│   └── lib.rs
└── tests
    └── integration_test.rs

Then we can create test in this folder and these tests may import our_crate as it will do it's final user: 

use our_crate;

#[test]
fn test_1() {
    // test some functionality from `our_crate`
}

References