Hi Chris - Let me comment on this from a more general point of view first, before going into the specifics. I've spent the last five years building a distributed system and during this time I've learned a couple of things about the value of timeouts :-) One thing that I've come to understand is that *no* operation is unbounded. We may leisurely talk about "just wait until it's done" but the reality is that regardless of what the operation is we never actually wait forever. At some point we *will* give up no matter what you may think. This is THE fundamental point here. Everything else is basically haggling about what the right timeout is. For the right timeout the second fundamental thing to understand is that if there's a question of whether the operation "maybe" completed, then your timeout is too short. Period. The timeout's value is not to indicate that "maybe" the operation completed, it is there to say unequivocally that something caused it to not complete and that it DID fail. Obviously, introducing timeouts will create some initial false positives. But it may be interesting to be a bit more precise on what we're talking about. To do this I attributed TestRunner to measure the time it takes to run each test and then ran all the tests in 4.2 to see where that leads us. As you might expect, the distribution is extremely uneven. Out of 2681 tests run 2588 execute in < 500 msecs (approx. 1800 execute with no measurable time); 2630 execute in less than one second, leaving a total of 51 that take more than a second and only three tests actually take longer than 5 seconds and they are all tagged as such. As you can see the vast majority of tests have a "safety margin" of 10x or more between the time the test usually takes and its timeout value. Generally speaking, this margin is sufficient to compensate for "other" effects that might rightfully delay the completion of the test in time. If you have tests that commonly vary by 10x I'd be interested in finding out more about what makes them so unpredictable. So if your question is "are my timeouts to tight" one thing we could do is to introduce the 10x as a more or less general guideline for executing tests, and perhaps add a transcript notifier if we ever come closer than 1/3rd of the specified timeout value (i.e., indicating that something in the nature of the test has changed that should be reflected in its timeout). This would give you ample warning that you need to adjust your test even if it isn't (yet) failing on the timeout. That said, a couple of concrete comments to your post: On 5/30/2010 11:52 AM, Chris Muller wrote:
(Copying squeak-dev too).
I'm not sold on the whole test timeout thing. When I run tests, I want to know the answer to the question, "is the software working?"
Correct.
Putting a timeout on tests trades a slower, but definitive, "yes" or "no" for a supposedly-faster "maybe". But is getting a "maybe" back really faster? I've just incurred the cost of running a test suite, but left without my answer. I get a "maybe", what am I supposed to do next? Find a faster machine? Hack into the code to fiddle with a timeout pragma? That's not faster..
See above. If you're thinking "maybe", then the timeout is too short.
But, the reason given for the change was not for running tests interactively (the 99% case), rather, all tests form the beginning of time are now saddled with a timeout for the 1% case:
As the data shows, this is already the case. It may be interesting to note that so far there were a total of 5 (five) places that had to be adjusted in Squeak. One was a general place (the default timeout for the decompiler tests) and four were individual methods. Considering that computers usually don't become slower over time, it seems unlikely that further adjustments will be necessary here. So the bottom line is that the changes required aren't exactly excessive.
"The purpose of the timeout is to catch issues like infinite loops, unexpected user input etc. in automated test environments."
If tests are supposed to be quick (and deterministic) anyway, wouldn't an infinite loop or user-input be caught the first time the test was run (interactively)? Seriously, when you make software changes, we run the tests interactively first, and then the purpose of night-time automated test environment is to catch regressions on the merged code.
These changes are largely intended for automated integration testing. I am hoping to automate the tests for community supported packages to a point where there will be no user in front of the system. Even if there were, it's not clear whether that person can fix the issue immediately or whether the entire process is stuck because someone can momentarily not fix the problem at hand and the tests will never run to completion and produce any useful result. So the idea here is not that unit tests are *only* to catch regressions in previously manually tested (combinations of) code. The idea is to catch interactions, and integration bugs and be able to produce a result even if there is no user to watch the particular combination of packages being loaded together in this particular form. Perhaps that is our problem here? It seems to me that you're taking a view that says unit tests are exclusively for regression testing and consequently there is no way a previously successful test would suddenly become unsuccessful in a way that makes it time out ... but you know, having written this sentence, it makes no sense to me. If we'd know beforehand that tests fail only in particular known ways we wouldn't have to run them to begin with. The whole idea of running the tests to catch *unexpected* situations and as a consequence there is value of capturing these situations instead of hanging and producing no useful result.
In that case, the high-level test-controller which spits out the results could and should be responsible for handling "unexpected user input" and/or putting in a timeout, not each and every last test method..
Do you have such a "high-level test-controller"? Or do you mean a human being spending their time watching the tests run to completion? If the former, I'm curious as to how it would differ from what I did. If the latter, are you volunteering? ;-)
IMO, we want short tests, so let's just write them to be short. If they're too long, then the encouragement to shorten them comes from our own impatience of running them interactively. Running them in batch at night requires no patience, because we're sleeping, and besides, the batch processor should take responsibility for handling those rare scenarios at a higher-level..
The goal for the timeouts is *not* to cause you to write shorter tests. If you're looking at it this way you're looking at it from the wrong angle. Up your timeout to whatever you feel is sensible to have trust in the results of the tests. As I said earlier, I'm quite happy to discuss the default timeout; it's simply that with some 95% coverage on a 10x safety margin it feels to me that we're playing it safe enough for the remaining cases to have explicit timeouts. Cheers, - Andreas