Macro relm_test::relm_observer_wait

macro_rules! relm_observer_wait {
    (let $($variant:ident)::*($name1:ident, $name2:ident $(,$rest:ident)*) = $observer:expr) => { ... };
    (let $($variant:ident)::*($name:ident) = $observer:expr) => { ... };
    (let $($variant:ident)::* = $observer:expr) => { ... };
}