How to mock out the world in C++ unit tests?

I can write a test in C++ with “IMPLEMENT_SIMPLE_AUTOMATION_TEST”, and this works great for anything simple.

But as soon as I test a class which has dependencies, or calls out to the world like with SpawnActor<>, my test of course blows up because the world does not exist.

How do most people get around this type of problem, given concepts like IOC are not strongly support?