There is a lot of disagreement about what is a unit test outside the realms of academia. The way I'm suggesting may lead to overlapping tests with subcomponents

There is a lot of disagreement about what is a unit test outside the realms of academia. The way I'm suggesting may lead to overlapping tests with subcomponents but I would argue that this is OK. If you have a car and you want to write a unit test for the wheel, does it make sense to stub out the tire? Or if you have a door, should you stub out the door handle in your unit test? I would say no because a good test is still about the functionality of the unit/component. Testing higher level components doesn't stop you from also writing tests for the tire or for the door handle. If the higher level components have a well abstracted interface, then you should be able to substitute any child component with any other working component later and the higher level component tests should still work without any changes required. You can even change the interface of children/sub-components; doesn't matter, the parent component tests keep working. Note that this is not true if you stub out the children, you need to keep updating the stubs.