Question

        class TestGet : public ::testing::Test 
        {
        protected:
            TestGet() 
                : _txHandle(11)
            {
                _interface.get = mockGet;
            }

            Interface_T _interface;
            Handle_T _txHandle;
            DB _db;
        };

If I change DB so that it only has the following constructor:

        explicit DB(Interface_T& _interface):
            _interface(interface)
        {
        }

Do I now need to declare _db using a std::shared_ptr in my TestGet class, initialising it with _interface in the constructor?

UPDATE:

The issue was that I had:

    private:
        Interface_T _interface;

in the DB class instead of a reference.

Answer 1

This should work:

TestGet()
: _interface()
, _txHandle(11)
, _db(_interface)
{
    _interface.get = mockGet;
}

It depends, though, whether the constructor of DB does anything non-trivial. As long as it just stores the reference, this should be fine. That is, DB should look like this:

struct DB
{
    Interface_T & _interface;
    explicit DB(Interface_T & interface) : _interface(interface) { }
};

If you need further initialization, you could either add an init() function to DB, or make an initialization function for Interface_T that you can use in the constructor of TestGet.