When developing in Rust, it’s essential to test our code efficiently to ensure reliability and correctness. An arsenal of testing tools is provided within the language that allows developers to maintain rigorous standards. However, as projects grow in size, it's not always practical or efficient to run all tests every single time. In these scenarios, knowing how to filter and select specific tests to run can save time and resources.
Understanding Rust’s Testing Framework
Rust’s built-in testing framework simplifies the testing process by integrating directly into the language. Standard Rust tests are implemented as functions that utilize the #[test] attribute. By running cargo test, these functions are automatically executed. Here is the simplest form of a test in Rust:
#[cfg(test)]
mod tests {
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
}
Running tests with cargo test executes all tests in your project. But what if you want to run a specific test? That’s where filtering and selection come into play.
Filtering Tests by Name
One of the easiest ways to narrow down the number of tests run is by providing a pattern that matches the name of the tests you wish to execute. For example, suppose we extend our test module:
#[cfg(test)]
mod tests {
#[test]
fn test_addition() {
assert_eq!(1 + 1, 2);
}
#[test]
fn test_subtraction() {
assert_eq!(2 - 1, 1);
}
}
To run only the test for addition, you would use the following command:
cargo test test_addition
This will execute only the tests that contain the substring "test_addition" in their names. Similarly, any partial match will run tests with names that include that pattern.
Running Ignored Tests
Sometimes, there are tests that may take too long to run under normal circumstances, so we mark them as ignored to exclude them from standard test execution. To achieve this, the #[ignore] attribute is used:
#[cfg(test)]
mod tests {
#[test]
#[ignore]
fn expensive_test() {
// Simulate a heavy computation
assert_eq!( expensive_computation(), true);
}
}
cargo test will not run expensive_test by default. However, you can include ignored tests during execution like so:
cargo test -- --ignored
By separating tests in this manner, it's easy to manage test execution based on context or necessity.
Grouping Tests with Test Suites
While filtering by name is a straightforward method, Rust also allows you to organize tests into test suites for better structure and control. Test suites can be implemented using submodules or different files in the tests directory for integration tests:
// src/lib.rs
#[cfg(test)]
mod integration_tests {
mod suite1 {
#[test]
fn basic_test() {
assert!(true);
}
}
mod suite2 {
#[test]
fn complex_test() {
assert!(1 + 1 == 2);
}
}
}
This setup allows selective execution of test sets by running:
cargo test suite1
This command will only run the tests included in suite1, showcasing efficient test management for larger projects.
Conclusion
Mastering the filtering and selection of tests can significantly enhance productivity and performance in Rust development. By tailoring test runs to focus only on relevant sections of code, developers can expedite the feedback loop, helping maintain high standards without sacrificing time. Utilize these techniques in conjunction with Rust’s powerful cargo tool to develop more efficiently and focus resources where they are most needed.
