gistfile1.cpp

class ExternalRouter
{
  private:
    static ExternalRouter *_instance;
    
  protected:
    ExternalRouter();
    
  public:
    static ExternalRouter *instance();
    static void setTestingInstance(ExternalRouter *newInstance);
}

void ExternalRouter::setTestingInstance(ExternalRouter *newInstance)
{
  delete _instance;
  _instance = newInstance;
}

class TestingExternalRouter : public ExternalRouter
{
  public:
  virtual void Dispatcher *getDispatcher() const {
    return new FakeDispatcher();
  }
}