Dub pre-build hook

[Chris Wright via Digitalmars-d-learn]

Is there a way to write a pre-build hook in Dub?

Specifically, I want to write unittests in a separate package to the rest 
of my source code. This requires a module that imports all my unittest 
modules. It's safer to automatically generate this than to rely on my 
memory.

My other alternative is to write a D script that assembles this file and 
then invokes dub, and always invoke dub via that script.