Rust Testing Skill

Master comprehensive testing in Rust: unit tests, integration tests, doc tests, property testing, and mocking.

Quick Start

Unit Tests

pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

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

    #[test]
    fn test_add_positive() {
        assert_eq!(add(2, 3), 5);
    }

    #[test]
    fn test_add_negative() {
        assert_eq!(add(-1, -1), -2);
    }

    #[test]
    #[should_panic(expected = "overflow")]
    fn test_overflow() {
        panic!("overflow");
    }

    #[test]
    #[ignore]
    fn expensive_test() {
        // Run with: cargo test -- --ignored
    }
}

Integration Tests

// tests/integration_test.rs
use my_crate::public_api;

#[test]
fn test_full_workflow() {
    let result = public_api::process("input");
    assert!(result.is_ok());
}

mod common;  // tests/common/mod.rs

#[test]
fn test_with_setup() {
    let ctx = common::setup();
    // test...
}

Doc Tests

/// Adds two numbers.
///
/// # Examples
///
/// ```
/// let result = my_lib::add(2, 2);
/// assert_eq!(result, 4);
/// ```
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

Test Commands

cargo test                      # All tests
cargo test test_name            # Specific test
cargo test -- --nocapture       # Show output
cargo test -- --ignored         # Ignored tests
cargo test --doc                # Doc tests only
cargo nextest run               # Fast parallel

Common Patterns

Async Tests

#[tokio::test]
async fn test_async_operation() {
    let result = async_function().await;
    assert!(result.is_ok());
}

Property Testing

use proptest::prelude::*;

proptest! {
    #[test]
    fn test_commutative(a in 0i32..1000, b in 0i32..1000) {
        assert_eq!(add(a, b), add(b, a));
    }
}

Mocking

use mockall::automock;

#[automock]
trait Database {
    fn get(&self, id: u32) -> Option<String>;
}

#[test]
fn test_with_mock() {
    let mut mock = MockDatabase::new();
    mock.expect_get()
        .returning(|_| Some("data".to_string()));
}

Troubleshooting

Resources

• Rust Book Ch.11
• proptest
• mockall