如何使用谷歌测试/模拟测试基于 MFC CWnd 的类？

Question

I am new with the idea of TDD. I have not used any testing framework before. Recently I have started reading about it and practicing with google test. My goal is to start TDD in a legacy code base developed in MFC. Most of the time I have to work with GUI controls - developing new custom controls, adding features to existing custom controls etc. So, I want to automate the testing of GUI classes which are mostly derived from CWnd class.

I have created a win32 console project in Visual Studio for testing, while creating the project I have ticked MFC in 'Add common header files for' option. Visual Studio project wizard has generated the main function and have created a CWinApp object. In the main function I have added the boilerplate code for google test. I have compiled the actual project (that is to be tested) and google test (and mock) library as .lib and linked it to the test project. I have successfully build the test project. I can test simple things from the projects.

Here is wizard generated code (google test boilerplate code included)-

#include "stdafx.h"
#include "TestMFC.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// The one and only application object
CWinApp theApp;
using namespace std;

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
    int nRetCode = 0;

    HMODULE hModule = ::GetModuleHandle(NULL);

    if (hModule != NULL)
    {
        // initialize MFC and print and error on failure
        if (!AfxWinInit(hModule, NULL, ::GetCommandLine(), 0))
        {
            // TODO: change error code to suit your needs
            _tprintf(_T("Fatal Error: MFC initialization failed\n"));
            nRetCode = 1;
        }
        else
        {
            // TODO: code your application's behavior here.
              testing::InitGoogleMock(&argc, argv);
              nRetCode = RUN_ALL_TESTS();
        }
    }
    else
    {
        // TODO: change error code to suit your needs
        _tprintf(_T("Fatal Error: GetModuleHandle failed\n"));
        nRetCode = 1;
    }
    return nRetCode;
}

The challenge I am facing is I can't create actual window as that will require to have message loop. I wanted to mock CWnd so that I can test features based on know assumptions. But, I can't find a way to mock CWnd as it has some non-virtual member functions that depend on HWND. HWND is valid only if I create a window. Another challenge is message handlers are not virtual functions. So I can't mock message handlers and without creating a window it is not possible to route a message to its handler.

I need thoughts on how can I approach to solve the problem. Can I do it without creating actual window with mock or something else? Or I can create window and route messages?

Thanks in advance.

Answer 1

I'd suggest using Visual Studio Coded UI Test Automation suite. It is much better than Google Mock. The Visual Studio Coded UI Test natively supports MFC/Win32 GUI stuff.

Answer 2

There is a problem with testing MFC application as most of the functions are not exported. So we should include our sources with GTEST project and link it with MFC runtime. And this is the tricky part. I've used VS2017 "Test Adapter For Google Test" with NuGet package: "googletest.v140.windesktop.static.rt-dyn" in my project and it finally works.

Answer 3

Chances are you need mfc and the message loop. It's easier to start with a Visual Studio wizard generated application and override the InitInstance, OnIdle and ExitInstance virtual functions of CWinApp.

You will probably need to allow windows messages to be carried via the MainWindow, so this gives you the ability to have a finite state machine (FST) running the tests. I initialised my environment in InitInstance and reported test results from ExitInstance. I used the FST mainly to setup the next test validator (a function pointer) (to be called from whatever was being actioned by the tested subject) and to call a test initiator function to send a message to initiate the next action.

I used OnIdle to start the testing as it was only consistently called when the MFC system had stabilised and setup.

The disadvantage of using googletest or Boost test or older versions of Visual Studio is that the unit test framework expects to drive the tests. They don't allow you to provide a FST to run the tests. I had issues with having my code in a DLL (global functions don't look at the same global address space in different DLLs - re Singleton pattern issues in DLLs).