Get a basic first test working, and lots of changes to supporting code to facilitate this

backend/test_utils/src/lib.rs

@@ -1,8 +1,10 @@
-// A helper to spawn or connect to shard/core processes and hand back connections to them
-pub mod connect_to_servers;
+/// Create/connect to a server consisting of shards and a core process that we can interact with.
+pub mod server;
+
+/// Test support for deserializing feed messages from the feed processes. This basically
+/// is the slightly-lossy inverse of the custom serialization we do to feed messages.
+pub mod feed_message_de;
 
 /// A wrapper around soketto to simplify the process of establishing connections
+/// and sending messages. Provides cancel-safe message channels.
 pub mod ws_client;
-
-/// A helper to construct simple test cases involving a single shard and feed.
-pub mod test_simple;