Function mock_service 

pub fn mock_service<S, I, F>(
    name: &'static str,
    state: S,
    f: F,
) -> (Addr<I>, JoinHandle<S>)
where
    S: Send + 'static,
    I: Interface,
    F: FnMut(&mut S, I) + Send + 'static,

Spawns a mock service that handles messages through a closure.

Note: Addr must be dropped before handle can be awaited.