Continuous Testing Explained

Continuous Testing Explained 105

Posted by Ben Rady Thu, 20 Sep 2007 21:11:00 GMT

What is continuous testing? It’s turning the knob on Test Driven Development up to 11, by automatically running the tests on every save. This has profound effects on the way that TDD is applied, and is likely to make you a more efficient and productive programmer.

First, a little history…

The term “Continuous Testing” was originally coined by the Program Analysis Group at MIT. Their research found, among other things, that “Developers using continuous testing were three times more likely to complete the [assigned] task before the deadline than those without” and that “continuous testing reduced wasted time [related to testing] by 92â€“98%.” These benefits come from a number of interesting effects:

Less Overhead

The first and most obvious effect of continuous testing is that you don’t have to manually run the tests. One less button to push…that’s always a good thing.

Defect Lag Reduced

Just as modern Java IDEs like IntelliJ and Eclipse increase feedback and productivity though continuous compilation, continuous testing reduces the time between the introduction of an error and it’s detection. This leads to more effective regression testing, because it’s not the expected failures that cost you time, it’s the unexpected ones. Continuous testing finds unexpected failures right away.

Promotes Good TDD Habits

If you’re running the tests on every save, it makes it more difficult to wander off the TDD path. Even though many of the participants in the MIT study were not versed in TDD, several of them reported that they â€œgot a small part of [their] code working before moving on to the next section, rather than trying to debug everything at the end.â€ Another remarked, â€œIt was easier to see my errors when they were only with one method at a time.â€ Making incremental changes is a core Agile principle, and directly reflected in the practice of TDD. Continuous testing makes the benefits of incremental development immediately apparent.

Tests Stay Fast

Using continuous testing helps keep your tests fast. This is something that was not mentioned in the MIT study, but I can attest to it in my own work. If you write a slow test, you’ll know right away, and you’ll probably have a good idea exactly what is making the test slow (because you just added it). I think the reason that they didn’t mention it in the MIT study is that they weren’t working with legacy code, or external systems, which is where a lot of test slowness comes from.

Today, there are a number of tools that support continuous testing:

CT-Eclipse (was Continuous Testing Plugin for Eclipse) – Java/Eclipse
ZenTest::Autotest – Ruby
Fireworks – Java/IntelliJ
Infinitest – Java

For full disclosure, I should mention that I’m the admin of the Infinitest project. Our goal is to create a continuous test runner for every development platform. We’ve already released a Java test runner, and we’re nearing completion of a Python runner.

Continuous testing is a practice that I have followed in my own work for most of 2007. There is little doubt in my mind that it is the future of TDD. Looking forward to the days of multicore systems, continuous testing may be an effective way to realize productivity improvements through better hardware. So long as they are independent (as they should be), test runs can easily be distributed across multiple cores, and perhaps even, multiple machines.

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Samuel A. Falvo II about 5 hours later:

I’ve been doing this for years, but not because I’m smarter than anyone else. It was borne out of pure laziness. Having to edit a file, then exit, then “make check” is pretty quick, but considering how fast development runs can be, it still becomes a burden. So, I use plain shell scripts to automate the task for me.

If you prefer to keep your editor running as you hack on code, I’m sure a vim- or elisp-script can be written to implement the desired behavior (assuming you’re using either vim or emacs). You do not need to use a special purpose IDE.
Erik about 6 hours later:

<fun about typo>
Did you really mean “continuous complication”? I’d vote for “continuous compilation”.

Probably a Freudian slip – if so, you should talk to your analyst about your relationship with your IDE ;-) Or was it just some brainless editor trying to correct a typo?
</fun about typo>
Besides that, I totally agree with you on the topic.
Ben about 17 hours later:

Erik – Wow, yeah, that takes on a whole new meaning…

Ha!

Let me fix that….
Peter Lawrey 1 day later:

We use continous integration and release so that successful releases are immediately available as snapshots to other projects.

We also use conditional checkin. What this does is perform a number of builds using the build server with the proposed changes and gives you the option of checking it in iff the builds all pass. This means you can do checkins and go to lunch or go home if it breaks a build, the checkin fails.
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ct-eclipse seems to be dead and the only installation instructions page is broken… http://ct-eclipse.tigris.org/install.html
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ShAaNiG over 3 years later:

Erik – Wow, yeah, that takes on a whole new meaning…

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We also use conditional checking. What this does is perform a number of builds using the build server with the proposed changes and gives you the option of checking it in if the builds all pass. This means you can do checking and go to lunch or go home if it breaks a build, the checking fails.

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We also use conditional checking. What this does is perform a number of builds using the build server with the proposed changes and gives you the option of checking it in iff the builds all pass. This means you can do checking and go to lunch or go home if it breaks a build, the checking fails.

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I agree that one less button to push is a good thing. I would have thought of a different meaning for continuous meaning if you have not explained it clearly. I would have thought it something negative and tedious.

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Continuous testing is a practice that I have followed in my own work for most of 2007. There is little doubt in my mind that it is the future of TDD. Looking forward to the days of multicore systems, continuous testing may be an effective way to realize productivity improvements through better hardware. So long as they are independent (as they should be), test runs can easily be distributed across multiple cores, and perhaps even, multiple machines.cheap VPS
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Developers typically run some subset of the unit tests with every compile as they are writing the software. This actually speeds up the development work since the tests help to find any logic errors in the code you’re working on. The idea of continuous testing is that the best way to make sure that the unit tests are run “with every compile”, and to get the benefits of doing so, is to make an automated daemon responsible for doing so.
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Hi Ben,

I was writing on ‘Continuous Testing’ as I am a tester so lot of questions popped in my mind. I think developer’s do most of the time checking. Like they check the output of some function or sometime if there is any change then the check if it is not changing existing functionality. I think instead of saying ‘Continuous Testing’ it should be ‘Continuous Unit testing’ :-) Because ‘Testing is very vast term. What say?
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