None of the Google Books links work for me, though. They just link to the same front-page of a book cover and some blurbs. Maybe old-fashioned citations are necessary. Certainly not including the right to pee during work.
Resource Leaks I've enjoyed watching ThoughtWorks tackle many difficult enterprise applications, bringing successful deliveries to many clients who have rarely seen success.
Our experiences have been a great demonstration that agile methods, deeply controversial and distrusted when we wrote the manifesto a decade ago, can be used successfully.
There are many flavors of agile development out there, but in what we do there is a central role for automated testing. Automated testing was a core approach to Extreme Programming from the beginning, and that philosophy has been the biggest inspiration to our agile work.
So we've gained a lot of experience in using automated testing as a core part of software development. Automated testing can look easy when presented in a text book. And indeed the basic ideas are really quite simple. But in the pressure-cooker of a delivery project, trials come up that are often not given much attention in texts.
As I know too well, authors have a habit of skimming over many details in order to get a core point across. In my conversations with our delivery teams, one recurring problem that we've run into is tests which have become unreliable, so unreliable that people don't pay much attention to whether they pass or fail.
A primary cause of this unreliability is that some tests have become non-deterministic. A test is non-deterministic when it passes sometimes and fails sometimes, without any noticeable change in the code, tests, or environment.
Such tests fail, then you re-run them and they pass. Test failures for such tests are seemingly random. Non-determinism can plague any kind of test, but it's particularly prone to affect tests with a broad scope, such as acceptance or functional tests.
Why non-deterministic tests are a problem Non-deterministic tests have two problems, firstly they are useless, secondly they are a virulent infection that can completely ruin your entire test suite.
As a result they need to be dealt with as soon as you can, before your entire deployment pipeline is compromised. I'll start with expanding on their uselessness. The primary benefit of having automated tests is that they provide bug detection mechanism by acting as regression tests .
When a regression test goes red, you know you've got an immediate problem, often because a bug has crept into the system without you realizing. Having such a bug detector has huge benefits. Most obviously it means that you can find and fix bugs just after they are introduced.
Not just does this give you the warm fuzzies because you kill bugs quickly, it also makes it easier to remove them since you know the bug got in with the last set of changes that are fresh in your mind. As a result you know where to look for the bug, which is more than half the battle in squashing it.
The second level of benefit is that as you gain confidence in your bug detector, you gain the courage to make big changes knowing that when you goof, the bug detector will go off and you can fix the mistake quickly.
The trouble with non-deterministic tests is that when they go red, you have no idea whether its due to a bug, or just part of the non-deterministic behavior. Usually with these tests a non-deterministic failure is relatively common, so you end up shrugging your shoulders when these tests go red.
Once you start ignoring a regression test failure, then that test is useless and you might as well throw it away.
If you have a suite of tests with 10 non-deterministic tests in them, than that suite will often fail. Initially people will look at the failure report and notice that the failures are in non-deterministic tests, but soon they'll lose the discipline to do that.
Once that discipline is lost, then a failure in the healthy deterministic tests will get ignored too.
At that point you've lost the whole game and might as well get rid of all the tests. Quarantine My principal aim in this article is to outline common cases of non-deterministic tests and how to eliminate the non-determinism.Your first challenge in writing a how-to essay is deciding on a topic.
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