Mailman 3 November 2018 - Twisted

[Twisted-Python] carly: a tool for testing twisted protocols with real networking
by Chris Withers 16 Nov '18

16 Nov '18

Hi All, Okay, so, I've started working jml's "really disconnecting" blog post into a more generic set of tooling for testing protocols talking to each other over real networking like this: https://github.com/cjw296/carly/blob/master/tests/test_line_receiver_server… Very interested in peoples thoughts, and especially if you can spot any bugs in these two: https://github.com/cjw296/carly/blob/master/carly/hook.py https://github.com/cjw296/carly/blob/master/carly/context.py Thanks for all the help so far, it's certainly helping me get my head around this all :-) Chris PS: Real networking is bad, yes, I know: slow, unreliable, etc ;-) However, in most of the testing I do, I end up having to hit a real database server to check my code works with it, so a few more tcp connections to localhost is not the end of the world!

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[Twisted-Python] "disconnecting properly" in tests still hangs on macOS
by Chris Withers 16 Nov '18

16 Nov '18

Right, so, I've been trying to get the technique in https://jml.io/pages/how-to-disconnect-in-twisted-really.html to work for me. No hating please, most of my testing in the past has involved hitting a relational database, so there's already a TCP connection flying around, one more won't make any difference. jml's example, exactly as-is on that page, hangs around 30-40% of the time when running on my macOS laptop. From changing the teardown to look like this: def tearDown(self): ds = defer.maybeDeferred(self.serverPort.stopListening) dc = defer.maybeDeferred(self.clientConnection.disconnect) print() ds.addCallback(lambda _: print('serverPort.stopListening')) dc.addCallback(lambda _: print('self.clientConnection.disconnect')) self.clientDisconnected.addCallback(lambda _: print('self.clientDisconnected')) self.serverDisconnected.addCallback(lambda _: print('self.serverDisconnected')) self.serverDisconnected.addErrback(lambda _: print('self.serverDisconnected:', _)) return defer.gatherResults([ds, dc, self.clientDisconnected, self.serverDisconnected]) ...it appears that it's the serverDisconnected deferred that's failing to fire. I can't reproduce this on Linux as of yet, so I'm guessing this is a difference between the SelectReactor used on macOS and the EPollReactor used on Linux. What's the best way to go about debugging a non-firing deferred like this? Anyone know what this might be? cheers, Chris

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Re: [Twisted-Python] pytest-twisted questions
by Chris Withers 14 Nov '18

14 Nov '18

On 13/11/2018 20:31, Kyle Altendorf wrote: > I would just open an issue on GitHub. Feel free to copy this in as the > first message to keep the initial context. Well, there's no specific issue to log here, so let's keep on going with email for now :-) (in fact, copying in the twisted mailing list, as that's probably the right place for this) > On 2018-11-13 12:35, Chris Withers wrote: >> - What's the intention of the plugin? Should all tests still subclass >> twisted.trial.unittest.TestCase or should they *never* do so if using >> this plugin? > > I don't know what _should_ be done, Victor, what was your intention with the project? > but I know that I mostly don't have > test classes and, for the class I do have, I didn't inherit. Mostly I > just @pytest.inlineCallbacks (I still don't like the namespace squashing > into pytest though :] ) and I suppose in the probably-not-too-distant > future I'll instead be using more @pytest_twisted.async_await (ala > #31/#34). Okay, but twisted.trial.unittest.TestCase does a bunch of reactor management stuff, most notable making you aware when you've left the reactor in a bad state. As far as I can see from the code, pytest-twisted does not do that, correct? >> - What's with the greenlet mentions? Is this plugin okay to use when >> I'm just using a normal Twisted epoll reactor? https://github.com/pytest-dev/pytest-twisted/blob/master/pytest_twisted.py#… https://github.com/pytest-dev/pytest-twisted/blob/master/pytest_twisted.py#… https://github.com/pytest-dev/pytest-twisted/blob/master/pytest_twisted.py#… https://github.com/pytest-dev/pytest-twisted/blob/master/pytest_twisted.py#… What does greenlet have to do with twisted in this context? Would be great to have it as an optional thing, unless I'm missing something? >> - What does pytest provide *without* this plugin, when it comes to >> testing with Twisted? > > I am not aware of anything twisted/pytest specific that is outside > pytest-twisted, https://docs.pytest.org/en/latest/faq.html#how-does-pytest-relate-to-twiste… So, my guess is that twisted.trial.unittest.TestCase subclasses unittest.TestCase and so pytest treats it in the same way. That means you get the management and checking of the reactor, along with the handy methods it provides, when you put your tests in class-based suites that subclass twisted.trial.unittest.TestCase. Ronny, does pytest do anything else that's twisted-specific? > If you are just trying to get started with something that works, I'd > skip the classes and inheritance and just let the reactor take care of > itself. My experience with Twisted over the last 10 years or so is that this is an exceedingly dangerous approach to take... cheers, Chris

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[Twisted-Python] Weekly Bug Summary
by trac＠twistedmatrix.com 11 Nov '18

11 Nov '18

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Re: [Twisted-Python] automated tests for a server application
by Kyle Altendorf 08 Nov '18

08 Nov '18

On 2018-11-06 11:28, Chris Withers wrote: > On 06/11/2018 12:14, Kyle Altendorf wrote: >> >> >> On November 6, 2018 6:41:23 AM EST, Chris Withers >> <chris(a)simplistix.co.uk> wrote: >>> 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#… >> >> What is 'fake' about this globally installed normally-the-default >> reactor? (Otherwise the qt5reactor if chosen) I guess I'm still not clear on what the point of using a 'fake' reactor over a 'real' one is. Not that I'm an expert here... > Nothing, but the technique could be used to install a fake reactor > rather than having to change all the existing code to accept an > optional reactor parameter. > >> I use @pytest_twisted.inlineCallbacks anyways, yes. >> >> Overall I'm not clear what was recommended here. Why fake the >> reactor? Even if not using a 'real client' wouldn't you just fake the >> data going through the connections rather than faking the entire >> reactor? > > I'd love to see some good example of faking the data going through the > connections, can you point me at some? I would assume you would just write a 'client' in the test of whatever complexity (could just write hardcoded byte sequences) which opens a connection to the server and transmits the bytes and then asserts things about the response. But no, I don't have any code. I can't say I have a good test suite myself and I also don't actually use Twisted for internet stuff (canbus and serial). Sorry. I would expect the servers provided by Twisted would have their own tests you could look at though. Cheers, -kyle

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[Twisted-Python] probably stupid question about automated testing and reactor.run
by Chris Withers 07 Nov '18

07 Nov '18

Hi All, Sorry, the silly questions about testing keep coming... Is it legit for a unit testable piece of an application's code to call reactor.run()? How do you feed a reactor.stop() into such a test? Would that be a sane thing to try and do? How do people deal with this kind of testing? cheers, Chris

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[Twisted-Python] "blocking" on a response to a client
by Chris Withers 06 Nov '18

06 Nov '18

Hi Again, So, separate question: I have a client that's making a connection to a websocket from a server. The client needs to send an "auth" message once the websocket is up, and the client code shouldn't progress until it receives an affirmative response. How do I do this in a non-blocking way when using twisted? (inside an inlineDeferred method in this case!) Similarly, how do I get this dance to happen again if the websocket drops? How would I do some kind of backoff on he connection retries? And, icing on the cake, where can I find good examples of how to write automated tests for all of the above? cheers, Chris

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Re: [Twisted-Python] automated tests for a server application
by Chris Withers 06 Nov '18

06 Nov '18

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#… > You can look at > https://twistedmatrix.com/documents/current/api/twisted.test.proto_helpers.… 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… ) > 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

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[Twisted-Python] automated tests for a server application
by Chris Withers 05 Nov '18

05 Nov '18

Hi All, (copying in Moshe as he expressed an interest!) I've inherited a twisted app for which I'd like to add some changes but want to improve the automated test coverage before I do. The app itself listens on a web socket (autobahn), an rpc port (RPyC) and also connects to a mysql database. So, for the automated tests, I want to check what happens when I send various messages to the websocket or rpc port, and then check what ends up in the db and what other state changes happen in the app itself. What's the best/correct way to write automated tests for this kind of situation? I'm using pytest and would happily use pytest-twisted too. Not keen to use trial... Any help is good help, pointers to nice existing examples would be fantastic! cheers, Chris

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[Twisted-Python] Weekly Bug Summary
by trac＠twistedmatrix.com 04 Nov '18

04 Nov '18

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