Question

I am trying to setup Agile and TDD environment for MFC applications that require high performance.

Since MFC View/Document are not testable, I am going to make them as dumb as possible and to test the other classes with Boost Test framework. – Please let me know if you know better way or better test framework for this environment.

In order to make TDD work, I think having dependency injection is crucial for loosely coupled structure. How can I achieve this? Any reference or hint will be appreciated.

Answer 1

Use shared_ptr’s to interfaces representing your classes.

I am thinking something like

#ifndef CLOCK_HPP_INCLUDED
#define CLOCK_HPP_INCLUDED

#include <boost/shared_ptr.hpp>


class Clock
{
public:
   static boost::shared_ptr<Clock> create();
   virtual void init() = 0;
   virtual double getSeconds() = 0;
   virtual void sleepUntilNext(double howMuch) = 0;

protected:  // No polymorphic deconstruction because of shared_ptr
   ~Clock()
   {}


};

#endif

Then you could just take the clock implementation in your constructor, or have another method to set the implementation, like setClock or something.

Example of this would be

#include "clock.hpp"
class MyClass
{
public: 
   myClass(boost::shared_ptr<Clock> aClock) : myClock(aClock)
   {
       myClock.init();
   }

private:
   boost::shared_ptr<Clock> myClock;
}  

Then in your unit testing you could do something like this:

boost::shared_ptr<Clock> mock = createMockClock();
MyClass b(mock);

mock.assertThatInitIsCalled();

You can also just ignore resources. The shared_ptr’s will delete themselves.

The cost to this would be a little performance loss due to dynamic allocation, virtual function calls, and the overhead of shared_ptr.

The benefits would be increased modularity, lowered compile time, easier use of mocking frameworks like googlemock(they require interfaces anyways), and easier resource management(you will never have a null pointer).