Macro assert_next_matches_with_timeout 

macro_rules! assert_next_matches_with_timeout {
    ($stream:expr, $pat:pat) => { ... };
    ($stream:expr, $pat:pat => $arm:expr) => { ... };
    ($stream:expr, $timeout_ms:expr, $pat:pat) => { ... };
    ($stream:expr, $timeout_ms:expr, $pat:pat => $arm:expr) => { ... };
}

Assert the next item in a Stream or Subscriber matches the provided pattern in the given timeout in milliseconds.

If no timeout is provided, a default 100ms value will be used.