Testing Guide

Tech Stack

• Test Framework: Standard #[test] / #[tokio::test]
• Mocking: mockall
• Async Testing: tokio-test

Test Structure

Unit Tests

Place in modules with #[cfg(test)]

// src/services/user_service.rs
pub struct UserService {
    repository: Arc<dyn UserRepository>,
}

impl UserService {
    pub async fn create(&self, data: UserData) -> Result<User> {
        // Implementation
    }
}

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

    #[tokio::test]
    async fn test_create_user_success() {
        // Test code
    }
}

Integration Tests

Place in tests/ directory

// tests/integration_test.rs
use my_app::prelude::*;

#[tokio::test]
async fn test_full_workflow() {
    // Integration test code
}

AAA Pattern

Arrange-Act-Assert pattern recommended

#[tokio::test]
async fn test_create_user_success() {
    // Arrange: Setup
    let mut mock_repository = MockUserRepository::new();
    mock_repository
        .expect_create_with_txn()
        .returning(|_, data| Ok(User {
            id: 1,
            name: data.name,
            email: data.email,
        }));

    let service = UserService::new(Arc::new(mock_repository));
    let user_data = UserData {
        name: "太郎".to_string(),
        email: "taro@example.com".to_string(),
    };

    // Act: Execute
    let result = service.create(user_data).await;

    // Assert: Verify
    assert!(result.is_ok());
    let user = result.unwrap();
    assert_eq!(user.name, "太郎");
    assert_eq!(user.email, "taro@example.com");
}

Mocking (mockall)

Trait Definition

use mockall::automock;

#[automock]
pub trait UserRepository: Send + Sync {
    async fn create_with_txn(
        &self,
        txn: &DatabaseTransaction,
        data: UserData,
    ) -> Result<User, RepositoryError>;

    async fn find_by_id(
        &self,
        txn: &DatabaseTransaction,
        id: i32,
    ) -> Result<Option<User>, RepositoryError>;
}

Using Mocks

#[tokio::test]
async fn test_with_mock() {
    // Create mock
    let mut mock_repo = MockUserRepository::new();

    // Set expectations
    mock_repo
        .expect_create_with_txn()
        .times(1)  // Called once
        .with(eq(txn), eq(user_data))  // Argument verification
        .returning(|_, data| Ok(User {
            id: 1,
            name: data.name,
            email: data.email,
        }));

    // Run test
    let service = UserService::new(Arc::new(mock_repo));
    let result = service.create(user_data).await;

    assert!(result.is_ok());
}

Multiple Call Mocks

#[tokio::test]
async fn test_multiple_calls() {
    let mut mock_repo = MockUserRepository::new();

    // Set multiple expectations
    mock_repo
        .expect_find_by_id()
        .times(2)
        .returning(|_, id| {
            if id == 1 {
                Ok(Some(User { id: 1, name: "太郎".to_string() }))
            } else {
                Ok(None)
            }
        });

    let service = UserService::new(Arc::new(mock_repo));

    let user1 = service.find_by_id(1).await.unwrap();
    assert!(user1.is_some());

    let user2 = service.find_by_id(2).await.unwrap();
    assert!(user2.is_none());
}

Error Case Mocks

#[tokio::test]
async fn test_error_case() {
    let mut mock_repo = MockUserRepository::new();

    // Mock returning error
    mock_repo
        .expect_create_with_txn()
        .returning(|_, _| Err(RepositoryError::DatabaseError("接続エラー".to_string())));

    let service = UserService::new(Arc::new(mock_repo));
    let result = service.create(user_data).await;

    assert!(result.is_err());
    match result.unwrap_err() {
        ServiceError::RepositoryError(_) => (),
        _ => panic!("Unexpected error type"),
    }
}

Running Tests

Commands

# Run all tests
cargo test

# Run specific test
cargo test test_create_user

# Show output
cargo test -- --nocapture

# Disable parallel execution
cargo test -- --test-threads=1

# Run integration tests only
cargo test --test integration_test

Debug

#[tokio::test]
async fn test_with_logging() {
    // Enable logging in test
    tracing_subscriber::fmt()
        .with_max_level(tracing::Level::DEBUG)
        .init();

    // Test code
    let result = service.create(data).await;

    // Debug output
    println!("Result: {:?}", result);

    assert!(result.is_ok());
}

Test Patterns

Success Case

#[tokio::test]
async fn test_success_case() {
    // Arrange
    let mock = setup_mock_success();

    // Act
    let result = function_under_test(mock).await;

    // Assert
    assert!(result.is_ok());
}

Failure Case

#[tokio::test]
async fn test_failure_case() {
    // Arrange
    let mock = setup_mock_failure();

    // Act
    let result = function_under_test(mock).await;

    // Assert
    assert!(result.is_err());
}

Boundary Value Testing

#[tokio::test]
async fn test_boundary_values() {
    // Empty string
    assert!(validate("").is_err());

    // Minimum length
    assert!(validate("a").is_ok());

    // Maximum length
    assert!(validate(&"a".repeat(255)).is_ok());

    // Maximum length + 1
    assert!(validate(&"a".repeat(256)).is_err());
}

Parameterized Tests

#[tokio::test]
async fn test_validation() {
    let test_cases = vec![
        ("", false),
        ("a", true),
        ("valid@example.com", true),
        ("invalid", false),
    ];

    for (input, expected) in test_cases {
        let result = validate_email(input);
        assert_eq!(result.is_ok(), expected, "Failed for input: {}", input);
    }
}

Best Practices

Test Names

// ✅ Good: Clear what is tested
#[tokio::test]
async fn test_create_user_with_valid_data_returns_user() { }

#[tokio::test]
async fn test_create_user_with_duplicate_email_returns_error() { }

// ❌ Bad: Vague
#[tokio::test]
async fn test1() { }

#[tokio::test]
async fn test_user() { }

Test Independence

// ✅ Create independent mocks per test
#[tokio::test]
async fn test_a() {
    let mock = MockRepo::new();
    // Test A
}

#[tokio::test]
async fn test_b() {
    let mock = MockRepo::new();
    // Test B (independent from test_a)
}

Assertion Messages

// ✅ Provide details on failure
assert_eq!(
    result.len(),
    expected_len,
    "User count mismatch. Expected: {}, Actual: {}",
    expected_len,
    result.len()
);

Common Patterns

Setup Helpers

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

    fn setup_mock_repository() -> MockUserRepository {
        let mut mock = MockUserRepository::new();
        mock.expect_create_with_txn()
            .returning(|_, data| Ok(create_test_user(data)));
        mock
    }

    fn create_test_user(data: UserData) -> User {
        User {
            id: 1,
            name: data.name,
            email: data.email,
            created_at: Utc::now(),
        }
    }

    #[tokio::test]
    async fn test_example() {
        let mock = setup_mock_repository();
        // Test code
    }
}

Async Tests

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

#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
async fn test_concurrent_operations() {
    // Concurrent test
}