Hi, I have added the test for SSEClient code. I'm not sure if I did it correctly or not. I added MockSSEClientAdapter() which is a subclass of MockAdapter. And I captured the actual event raw response and put it in payload. But somehow when I run the test, the MockSSEClient actually sends out Bytes object which is expected, but inside SSEClient code's response.iter_content returns bytes instead of string. I compared it with the my program to actually communicate with the server, and somehow iter_content returns string. Therefore for now, I added a check for the type in SSEClient, to call decode() if the nextchar from response.iter_content is a bytes object.

                nextchar = next(self.resp_iterator)
                if isinstance(nextchar, bytes):
                    nextchar = nextchar.decode()
                self.buf += nextchar

Python will raise TypeError: Can't convert 'bytes' object to str implicitly if executed the test withouth this check. Is there anyway to modify the MockSSEClientAdapter or the parent class, to make it's response.iter_content return string instead of bytes?
But I'm not sure about this check yet so I haven't committed this change. Please comment.