Writing unit tests which may access private/protectedstate

I use Boost Test for unit tests. I typically have a fixture struct:

class ClassBeingTested
{
protected:
    int _x;             // Want to access this directly in my unit tests
};

struct TestFixture : public ClassBeingTested
{
    // I can access ClassBeingTested::_x here but it means i have to add getters for each test to call
    ClassBeingTested _bla;
};

However, even if my fixture inherits from ClassBeingTested or uses a friend relationship I cannot access private/protected methods/state from each individual test:

BOOST_FIXTURE_TEST_CASE(test1, TestFixture)
{
    _bla.doSomething();
    BOOST_REQUIRE_EQUAL(_bla.x, 10);    // Compiler error. I cannot access ClassBeingTested::_x here
}

only the fixture, which means I have to add a new getter (or test) for each access I wish to make.

Is there any way to achieve this? I have to add public getter methods to ClassBeingTested which are only used by tests, which isn't ideal.

(Please no replies of 'test using the public interface', that's not always possible).