InMemoryMessagingNetwork(sendManuallyPumped: Boolean)
An in-memory network allows you to manufacture InMemoryMessagings for a set of participants. Each InMemoryMessaging maintains a queue of messages it has received, and a background thread that dispatches messages one by one to registered handlers. Alternatively, a messaging system may be manually pumped, in which case no thread is created and a caller is expected to force delivery one at a time (this is useful for unit testing).