Question

I have a Visual Studio 2008 C++ project where I am implementing unit tests for a class that uses a boost::asio::ip::udp::socket. To get to unit testability, I need to be able to pass in a Mock of that socket object.

My problem is that you can’t have a virtual template function and boost::asio has a heavily templatized user interface.

How does one create an interface to mock for a C++ library that uses templates?

// socket interface that can be mocked
class IUDPSocket
{
public:
    virtual void open( const boost::asio::ip::udp& protocol ) = 0;

    // problem!
    template <typename SettableSocketOption>
    virtual void set_option( const SettableSocketOption& option ) = 0;

    virtual void bind( const boost::asio::ip::udp::endpoint& endpoint ) = 0;

    // Problem! 
    template <typename MutableBufferSequence, typename ReadHandler>
    virtual void async_receive_from( 
        const MutableBufferSequence& buffers,
        boost::asio::ip::udp::endpoint& sender_endpoint,
        ReadHandler handler ) = 0;

protected:
    virtual ~IUDPSocket() = 0;
};

// socket class that will be used for "normal" operation.
class BoostUDPSocket
{
    // ...

    virtual void open( const boost::asio::ip::udp& protocol )
    {
        socket_.open( protocol );
    };

private:
    boost::asio::ip::udp::socket socket_;
}; 

If it matters, I am using Google Test as my unit test framework.

Thanks

Answer 1

Two possibilities:

1. Don’t use types from boost::asio in your interface directly, use abstraction if the types are complex enough: IMutableBufferSequence, IEndpoint etc…
2. Templatize your entire interface with respect to types used in the methods, but then the question is do you need a polymorphic type “interface” at all?