Help: Python unit testing

[Harsh Gupta]

Hello All,

I have been trying to write a test framework for a pretty simple command server application in python. I have not been able to figure out how to test the socket server.
I would really appreciate if you could help me out in testing this application using unittest. I'm new to this.
Please find the commandserver.py file . 

'''
import socket
import time

supported_commands = {'loopback', 'print', 'close'}

class CommandServer:

    def __init__(self, ip='localhost', port=5000):
        
        self.server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.server.bind((ip, port))

        print "Server running"
        self.is_running = True

    def start_listening(self, num_connections=2):
        self.server.listen(num_connections)
        self._accept()

    def is_running(self):
        return self.is_running
        
    def _accept(self):
        self.client, self.remote_addr = self.server.accept()
        
        print "Received connection from %s" % (self.remote_addr,)
        self.is_connected = True

    def _get_data(self, bufsize=32):
        try:
            return self.client.recv(bufsize)
        except KeyboardInterrupt:
            self.close()

    def wait_for_commands(self):
        while self.is_connected:
            cmd = self._get_data()
            if cmd:
                if cmd not in supported_commands:
                    print "Received unsupported command"
                    continue

                if cmd in ("loopback", "print"):
                    payload = self._get_data(512)

                if cmd == "loopback":
                    self.client.sendall(payload)

                elif cmd == "print":
                    print payload

                elif cmd == "close":
                    self.close()

    def close(self):
        self.client.close()
        self.server.close()
        self.is_connected = False
        print "Connection closed"

if __name__ == '__main__':
    
    cmd_server = CommandServer()    
    cmd_server.start_listening()
    cmd_server.wait_for_commands()

'''

The tests cases I came up with are:
1. Start the server
2. Establish connection with client
3. Test the server by sending 3 commands
    - loopback command should  send all payload.
    - print command should print payload
    - close command should close the connection between server and client.

4. Raise error if any other command is send other than listed 3 commands

Other nominal cases
1. Check if both the server and client are closed. It might happen that only one is closed.
2. Go to sleep/Cancel the connection if no command is received after a certain period of time.

Thank You

Harsh