Accessing functions of a class that implement an Interface that are not part of the Interface

I am writing an application in c++. I have an interface defined with various functions:

class ITest
{
public:
        virtual void x()=0;
        virtual void y()=0;
}

I then have a class t开发者_JAVA技巧hat implements this interface, along with additional functions:

class NewClass: public ITest
{
public:
    virtual void x();
    virtual void y();
    // new function not defined in interface
    virtual void z();
}

I now want to access all of these 3 functions from my unit tests. Currently I am using:

ITest* pTest;

which will only give me access to the 2 functions defined in the interface. How can I also gain access to function z() without defining it in the interface?

NewClass* p = dynamic_cast<NewClass*>(pTest);
if(p==0)
{
   //error!!! pTest's dynamic type wasn't NewClass*
}
else
{
   p->z();
}

Instead of dynamic_cast, you can use static_cast. But if pTest's dynamic type is not actually NewClass* you'll get undefined behavior.

Use a NewClass* or cast to one if it is one.

As it is an unit test, you control the line where the class is created.

Now don't do:

ITest* pTest = new NewClass();

but do:

NewClass* pTest = new NewClass();

and you can use pTest->z() without problems.