How do I unit test a factory?

Question

I unit test my classes by giving all my classes an interface. These interfaces have in turn their own mocks.

But lets say I have the following:

class IData
{
  GetData()
}

class IOnScreenDataCalculator
{
  Calculate(IData)
}

class OnScreenData : IOnScreenData
{
  OnScreenData(PTR_T(IData), PTR_T(IOnScreenDataCalculator))

    enter code here

  GetOnScreenData()
}

Now lets say that I wish to have a number of factories for different types of data and calculators. How can I unit test these factories where my factories are as follows:

OnScreenBlueDataForWideScreenFactory
{
  PTR:T(IOnScreenData) Create()
  {
    PTR_T(Data) data = ptr_t(new BlueData());
    PTR_T(IOnScreenDataCalculator) calculator = ptr_t(new WideScreenDataCalculator());
    PTR_T(IOnScreenData) onScreenData = ptr_t(new WideScreenDataCalculator(data, calculator ));

    return onScreenData;
  }
}

Thanks for your help,

Barry.

Answer 1

I am not sure the code snippets are really c++, but the example should be something like this :

class ExampleIface
{
  public:
    virtual ~ExampleIface() {}
    virtual void a() = 0;
};

class Example1: public ExampleIface
{
  public:
    virtual ~Example1() {}
    virtual void a()
    {
      // something
    }
};

class ExampleFactory
{
  public :
    typedef ExampleIface * ExamplePtrType; // can be shared_ptr instead

    static ExamplePtrType Create( /*params?*/)
    {
      ExamplePtrType p( new Example1 );
      return p;
    }

  private:
    ExampleFactory();
    ~ExampleFactory();
};

and the unit test:

void test_Create()
{
  ExampleFactory::ExamplePtrType p = ExampleFactory::Create();
  Example1 *realType = dynamic_cast< Example1* >( p );
  TS_ASSERT( NULL != realType ); // if you use cxxtest
}

Answer 2

I'd call Create() and verify that I get a properly constructed object with the right constituent types.