rust-bevy-test-conventions

Rust Bevy test conventions

Quick start

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

    fn setup() -> App {
        let mut app = App::new();
        app.add_plugins((MinimalPlugins, YourPlugin));
        app
    }

    #[test]
    fn system_produces_expected_output() {
        let mut app = setup();

        // Setup: Add resources and entities
        app.insert_resource(YourResource::default());

        // Action: Run the system
        app.update();

        // Assert: Verify results
        let resource = app.world().resource::<YourResource>();
        assert_eq!(resource.value, expected_value);
    }
}

Testing ECS systems

Integration-style approach

Test Bevy systems using full App instances with MinimalPlugins:

fn setup() -> App {
    let mut app = App::new();
    app.add_plugins((
        MinimalPlugins,
        YourPlugin,
        // Add other required plugins
    ));
    app
}

#[test]
fn player_input_system_sends_move_message() {
    let mut app = setup();

    // Setup state
    app.insert_resource(NextState::Pending(AppState::Playing));
    app.update(); // Apply state transition

    // Trigger system behavior
    app.world_mut().send_event(KeyboardInput {
        key_code: KeyCode::KeyW,
        state: ButtonState::Pressed,
        /* ... */
    });
    app.update();

    // Verify via message resource
    let messages = app.world().resource::<Messages<MoveMessage>>();
    assert!(!messages.is_empty());
}

Setup helper functions

Create a common setup() function to reduce boilerplate:

fn setup() -> App {
    let mut app = App::new();
    app.add_plugins((MinimalPlugins, ControlsPlugin, StatesPlugin));
    app.init_resource::<Messages<YourMessage>>();
    app
}

fn setup_with_player() -> App {
    let mut app = setup();
    app.world_mut().spawn(Player::default());
    app
}

State simulation

Use NextState to manually advance system states: