Unit testing D module

[Dfr]

If i do not want to unit test whole codebase, because it big 
enough and all tests take noticeable time to run.

So i trying this:
dmd -unittest mymodule.d

And getting error: "undefined reference to `main'"
But i don't want to run 'main' here, just unit test please.
Any idea how to test single module without putting 'main' in 
every module ?