[Twisted-Python] testing a tac file

[Jean-Paul Calderone]

On Mon, 29 Jun 2009 13:19:53 -0700, Rob Hoadley <hoadley at gmail.com> wrote:
>Hi, I'm curious if anyone has written a trial test to verify the
>correct startup of a .tac file.
>
>I have a buildbot running automated trial tests on all the services
>I've written but nothing that closes the loop by building up the
>services by running the tac file similarly to the way that you'd use
>trial.   Ideally, I'd like to verify that the MultiService has
>properly started up all the services from a list defined by the test.
>I know this a fairly nitpicking problem.  In production, It's easy for
>me to just ssh into the running process and see what's going on via
>the manhole.  But, I was hoping to catch a badly behaving tac file in
>the buildbot.  It may be something out of the scope of trial but I was
>hoping someone has some integration test approaches for a twisted
>project they could share.

This is definitely one of the big shortcomings of .tac files.  I generally
approach this by absolutely minimizing the amount of code in the .tac file
itself.  This doesn't help you test the code that's there, but if you're
limited to importing a function that creates your service, calling that
function, and attaching it to the application object, at least there's
very little code that's untested, and it should be modified very
infrequently.

I welcome any suggestions for a better answer than this one.  It would
probably be easy to make a case for the inclusion of some APIs to help
out tests.  `twisted.application.service.loadApplication´ might even
go towards this end already - I've never tried writing a test using it,
but maybe that would work out well.

Jean-Paul