Macro xcm_simulator::decl_test_relay_chain

macro_rules! decl_test_relay_chain {
    (
		pub struct $name:ident {
			Runtime = $runtime:path,
			RuntimeCall = $runtime_call:path,
			RuntimeEvent = $runtime_event:path,
			XcmConfig = $xcm_config:path,
			MessageQueue = $mq:path,
			System = $system:path,
			new_ext = $new_ext:expr,
		}
	) => { ... };
}

The macro is implementing upward message passing(UMP) for the provided relay chain struct. The struct has to provide the XCM configuration for the relay chain.

decl_test_relay_chain! {
    pub struct Relay {
        Runtime = relay_chain::Runtime,
        XcmConfig = relay_chain::XcmConfig,
        new_ext = relay_ext(),
    }
}