Running tests on Twisted code in Python3

Question

I've got a relatively simple SSL server running in Twisted and I'd like to write some unit tests for it. I'm not really sure the best way to do this when using Python 3. All the documentation I've found describes using Twisted Trial which unfortunately is incomplete for Py3k.

What I'm thinking is doing something like this:

• loading up my code and doing everything but reactor.run()
• send the data I want my code to handle
• run reactor.doIteration() (or maybe reactor.iterate() is better?)
• check that my server did what it was supposed to

Is this a legitimate way of handling this sort of situation?

EDIT:

answer from glyph that this may be a bad idea (but it's not specifically talking about testing)

EDIT 2:

I guess the major issue is when you're trying to test components intertwined with Twisted and you're not sure how to pull it apart to properly test the individual components. Is there any reliable way to test this? Should .run() be called and then insert an event that's run a few seconds after you've completed your action to stop the reactor and test the result?

Answer 1

Are you writing low-level networking code? Does your application interact with BSD socket APIs? If not, why do you want to run the reactor at all in your tests? Unit tests should exercise a well-defined, narrow set of code. This should be your application code - not the implementation of the TLS transport in Twisted.

To specifically address the idea of calling reactor.iterate, either in your unit tests or elsewhere: yes, it is a bad idea. This is not how Twisted itself is tested. There is no reason to expect that because you write code that works when you call reactor.iterate it will work when you call reactor.run instead. reactor.iterate is a left-over from a mistaken idea about how event loops should be integrated with other systems. There may be an extreme edge case or two where the idea of reactor.iterate is correct and useful but in practice no one uses Twisted in such cases and no one who works on Twisted bears them in mind when making changes. So this is not a place you want your application to be. When things go wrong you'll be very lonely.