[Twisted-Python] automated tests for a server application

[Chris Withers]

On 06/11/2018 05:43, Moshe Zadka wrote:
>
> Some of the best advice depends on details of the application. One 
> trick that is sometimes useful is passing in a "fake" reactor object. 
> This, of course, is only useful if the application is structured in a 
> way that functions/classes expect to get a reactor, instead of 
> reaching for the global one. However, usually *that's* not a 
> complicated refactoring to do.

Cool, do you have any example tests that do this?
Interesting, looks like pytest-twisted does away for the need for this 
by showing how to install a fake reactor globally:
https://github.com/pytest-dev/pytest-twisted/blob/master/pytest_twisted.py#L129-L142

> You can look at 
> https://twistedmatrix.com/documents/current/api/twisted.test.proto_helpers.MemoryReactor.html for 
> inspiration although, as all code under `twisted.test`, it is not 
> intended as end-user functionality, so using it directly is problematic. 

Not sure I fully understand this, why is the MemoryReactor bad to use? 
Where is it used?

> It would be nice to have externally-useful reactors along the lines of 
> Clock 
> (https://twistedmatrix.com/documents/current/api/twisted.internet.task.Clock.html ) 
> but, unfortunately, we do not have that yet.

So, clock is just a clock, right? How would that get worked into a 
"real" reactor for testing?

> You can, of course, use a real reactor and a real client to pump data. 
> However, in that case, you probably do want to switch to trial so that 
> you can return a deferred from a test function and have the reactor 
> run until the deferred fires. This is not great, but can work in a pinch.

pytest-twisted looks like it supports this pattern too, allowing test 
functions to return deferreds...

I guess I'm still really looking to see examples of all of this...

Chris