Rust Testing Skill

When to Activate

Activate this skill when:

• Writing Rust unit tests

• Creating integration tests

• Working with doc tests

• Setting up property-based testing

• Running benchmarks

Quick Commands

Run all tests

cargo test

With output

cargo test -- --nocapture

Run specific test

cargo test test_user_create

Run tests in module

cargo test auth::

Run ignored tests

cargo test -- --ignored

Doc tests only

cargo test --doc

Integration tests only

cargo test --test integration

Unit Tests (Same File)

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

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

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

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

}

Test Attributes

#[test] fn regular_test() { }

#[test] #[ignore] fn slow_test() { } // Skip unless --ignored

#[test] #[should_panic] fn test_panic() { panic!("This should panic"); }

#[test] #[should_panic(expected = "specific message")] fn test_panic_message() { panic!("specific message here"); }

#[test] fn test_with_result() -> Result<(), String> { let result = some_operation()?; assert_eq!(result, expected); Ok(()) }

Assertions

// Basic assert_eq!(1 + 1, 2); assert_ne!(1 + 1, 3); assert!(true);

// With messages assert_eq!(result, expected, "values should match: got {}", result);

// Pattern matching assert!(matches!(value, Pattern::Variant(_)));

// Option/Result assert!(some_option.is_some()); assert!(some_result.is_ok());

Integration Tests

// tests/api_integration.rs use my_crate::{Config, Server};

#[test] fn test_server_startup() { let config = Config::default(); let server = Server::new(config); assert!(server.start().is_ok()); }

Directory Structure

project/ ├── Cargo.toml ├── src/ │ ├── lib.rs # Unit tests in #[cfg(test)] │ └── user.rs # Module with inline tests └── tests/ # Integration tests ├── common/ │ └── mod.rs # Shared utilities └── api_test.rs

Mocking with Traits

pub trait UserRepository { fn find_by_id(&self, id: u64) -> Option<User>; }

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

struct MockUserRepo {
    users: HashMap<u64, User>,
}

impl UserRepository for MockUserRepo {
    fn find_by_id(&self, id: u64) -> Option<User> {
        self.users.get(&id).cloned()
    }
}

#[test]
fn test_user_service() {
    let mut users = HashMap::new();
    users.insert(1, User { id: 1, email: "test@example.com".into() });
    let repo = MockUserRepo { users };

    let service = UserService::new(Box::new(repo));
    let user = service.get_user(1).unwrap();
    assert_eq!(user.email, "test@example.com");
}

}

Async Testing (tokio)

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

#[tokio::test] async fn test_with_timeout() { let result = tokio::time::timeout( Duration::from_secs(5), slow_operation() ).await; assert!(result.is_ok()); }

Doc Tests

/// Adds two numbers together. /// /// # Examples /// /// /// use my_crate::add; /// let result = add(2, 3); /// assert_eq!(result, 5); /// pub fn add(a: i32, b: i32) -> i32 { a + b }

Property-Based Testing (proptest)

use proptest::prelude::*;

proptest! { #[test] fn test_add_commutative(a: i32, b: i32) { prop_assert_eq!(add(a, b), add(b, a)); } }

Coverage

Using cargo-tarpaulin

cargo install cargo-tarpaulin cargo tarpaulin --out Html

Using cargo-llvm-cov

cargo install cargo-llvm-cov cargo llvm-cov --html

Related Resources

See AgentUsage/testing_rust.md for complete documentation including:

• Benchmarking with criterion

• Setup/teardown patterns

• Mockall crate usage

• CI configuration