I have a BackgroundRb worker in charge of dispatching some emails.
How should I tell this worker not to run during tests? Does the framework include some configuration parameter or stub worker I could use?
MiddleMan.worker(:emails_worker).async_send_mails(:arg => {:emails => emails})
I would say stub it out in your tests.
If you are using rspec (sorry what I know best) then I would:
Middleman.stub!(:worker)
in your before block and it will let you call it, and you can test that it is called like so
Middleman.should_receive(:worker).with(YOUR_ARGS_HERE)
but it will not run.
On a side note I would also say that BackgroundRb is not up to date technology and there are much better background worker solutions now. I would say look into something like delayed job.