How to set up a mock server with GoogleMock - c++

Question

I am converting old C code to C++, and I am testing it as I rewrite with GoogleTest. Part of my code uses sockets to connect to a remote host, with an IPV4 address. I am having a lot of trouble understanding how I can use GoogleTest and GoogleMock to test the socket part of my code.
My object takes in a host IP address and number of seconds to wait before trying to connect to a host again. There is a function called "conn()" that actually tries to connect to the host. That is the function I want to test. So in my test, I want to do something like:
TEST(CONNECTION_TEST, Connection)
{
MyObject obj("###.###.###.###", 1);
ASSERT_TRUE(obj.conn());
}
I read on here that I needed to mock up a server since testing a remote host isn't really advisable. I am brand new to GoogleMock, so I read the official documentation and read the GoogleTest primer, GoogleMock For Dummies, the GoogleMock Cheat Sheet, and the GoogleMock Cookbook. I watched CodesBay's tutorial. I looked at several posts on SO, including What is wrong with my attempts to mock a simple C++ method with googlemock?, Patterns for unit testing a C++ method that makes a standard library call, and How to unit test BSD sockets.
For my mock server, I did the following. I made a Socket class that wraps socket.h, and then I extended MockSocket from it. In my TEST, I set up the mock socket to accept connections, like so:
TEST(CONNECTION_TEST, Connection)
{
// bind to local host?
MyObject obj("0.0.0.0", 1);
// create the host
MockSocket mock_sock;
MockSocket new_sock;
EXPECT_CALL(mock_sock, create()).Times(1);
EXPECT_CALL(mock_sock, bind(_));
EXPECT_CALL(mock_sock, listen());
EXPECT_CALL(mock_sock, accept(_));
mock_sock.create();
mock_sock.bind(123);
mock_sock.listen();
mock_sock.accept(new_sock);
ASSERT_TRUE(obj.conn());
}
As you can tell, I don't know what I am doing. My test results fail and I think it is because I just didn't do this correctly. Please, can someone guide me in the right direction? Is the mock server the correct way to test my object?

Answer 1

What do you want to test?
Do you want to test if the TCP/IP socket class (assuming there is one), can actually connect and communicate with some TCP/IP service? This is more an end-to-end test. You can use Google Test to do this, but you need a running TCP/IP service to communicate with. This is not where the Google mocking framework is for. This is similar to when you want to test a class that reads a file: you need to have a file that it can read and Google mocking framework will not help you here.
Do you want to test if some other class, that uses your TCP/IP socket class, works? Here you can use Google mocking framework to create a mock for your socket class. This mock will act as the socket class to your other class but will not do any TCP/IP communication. This way you can unit-test your other class.