Function run_loop_with 

pub fn run_loop_with(
    account: AccountConfig,
    paths: Paths,
    events: Sender<Event>,
    shutdown: Arc<AtomicBool>,
    commands: Receiver<Job>,
    wake: Arc<AtomicBool>,
    connect: impl FnMut() -> Result<Box<dyn MailOps>, SyncError>,
    sleep: impl FnMut(Duration),
)

The loop body, with connection and back-off sleeping injected so tests can drive it with the fake.