The goal of :metadata_integration_test is to make sure that drivers can send and receive metadata to each other using the //sdk/lib/driver/metadata/cpp library. The test will spawn a driver test realm and include the following four drivers: test_root, metadata_sender, metadata_forwarder, and metadata_retriever.
The test_root's purpose is to create nodes that the metadata_sender driver variants can bind to.
The metadata_sender's purpose is to serve metadata using fdf_metadata::MetadataServer. The driver has two variants: metadata_sender_expose which exposes the fuchsia.hardware.test.MetadataSenderService FIDL service in its component manifest and metadata_sender_no_expose which does not. It can also create nodes that the metadata_forwarder driver and metadata_retriever driver variants can bid to.
The metadata_retriever's purpose is to retrieve metadata via fdf_metadata::GetMetadata(). It has two variants: metadata_retriever_use which declares that the driver uses the metadata FIDL service in its component manifest and medatata_retriever_no_use which does not.
The metadata_forwarder's purpose is forward metadata using fdf_metadata::MetadataServer::ForwardAndServe(). The metadata_forwarder driver will create a child node that the metadata_retriever_use driver can bind to.