Use a simple python or perl script to fake the protocol.
Stop your ssh daemon on the server and then start up the Python script:
The RequestHandler class for our server.
It is instantiated once per connection to the server, and must
override the handle() method to implement communication to the
# self.request is the TCP socket connected to the client
self.data = self.request.recv(1024).strip()
print "%s wrote:" % self.client_address
# just send back the same data, but upper-cased
# Simulate error Here!
# maybe exit()
if __name__ == "__main__":
HOST, PORT = "localhost", 22
# Create the server, binding to localhost on port 9999
server = SocketServer.TCPServer((HOST, PORT), MyTCPHandler)
# Activate the server; this will keep running until you
# interrupt the program with Ctrl-C
Just tweak the script to get it to "fail" the way you want either not replying, sending rubbish back, or killing the listener process.