Enabling Only Top-Level Unittests

[Nordlöw via Digitalmars-d-learn]

I want to enable unittests only at the top-level of a module 
compilation.

If I have a module

     top.d

that imports

     dep1.d
     dep2.d
     ...

which all contain unittests, how do I compile top.d with only the 
unittests for top.d enabled?