The goal of :metadata-server-test is to make sure that drivers can send and retrieve metadata to each other using the ddk::MetadataServer class and ddk::GetMetadata() function. The test will spawn a driver test realm and include the following drivers: metadata_sender, metadata_forwarder, and metadata_receiver.
The metadata_sender driver's purpose is to serve metadata to it child devices using ddk::MetadataServer. It can create child devices named metadata_{num} (with {num} being a number) that the metadata_forwarder or metadata_retrievers drivers may bind to.
The metadata_forwarder driver's purpose is to retrieve metadata from its parent driver and forward the metadata to its child device using ddk::MetadataServer::ForwardAndServe(). It will create a child device that the metadata_retriever driver can bind to.
The metadata_retriever driver's purpose is to retrieve metadata using ddk::GetMetadata().