A C++ regression suite would be really, really useful to have. Though it's quite hard to do effectively because the protocol is so minimal - it's not possible, for example, to find out if a node accepted your block or tx except by doing some rather indirect tricks or using JSON-RPC which makes it only work for the C++ impl.
Maybe you could see if the other node broadcasts your transaction.
The test suite could be
- have the client under test connect to 2 other (known good) nodes
- send 1000 transactions to the node under test
- see which transactions it forwards and which it refuses to forward