Nested data driven tests

While this topic seems to be discussed many times, I still cannot quite grasp it. I care about the scenario when test A calls test B and both of them are data bound. When those tests use separate data sources it works as expected. But if I tick "Inherit parent Data Source" for test B, then.. I don't understand what is going on.

Actual scenario I'm trying to achieve is - test B normally has its own data source which supposed to be used when test B is run standalone, BUT when test B is invoked as part of a bigger test I want it to inherit parent's data source and use that one instead. HOW test A datasource should look like so that it serves both A and B in this case?

Is there decent downloadable example for this scenario?

Thank you!
Konstantin