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Note that this article is badly out of date.
2011 10 26 Use version 3.5.15 of PHPUnit. Please see reference material on github.
2009 10 06: Tests now depend on the SVN version of PHPUnit 3.4.1.
2008 06 24: Update to reflect move of PHPUnit code from branch to trunk (former trunk now in /branches/old_simpletest).
2008 06 22: Add information on limiting tests by version.
2008 06 21: Added—class-exclude, --sequence-exclude, and—test-exclude options.
2008 06 21: PHPUnit has been updated to version 3.2.21 with SVN rev 10436. Please update.
Unit testing is not only an essential part of a good Quality Control program, it is an aid to development as well. Writing new tests before writing code helps focus the developer on the problem at hand. The practice also encourages writing smaller, more loosely coupled, more reusable, and more maintainable code units and these benefits often outweigh the benefits gained by treating unit tests solely as a QC tool. When used in this manner correctness becomes more a by-product of the process than the goal. For a good general discussion of unit testing, visit the Wikipedia article.
Open source projects, with multiple developers working in parallel around the world, can greatly benefit from unit testing. The main benefits are:
Software testing systems usually run through a spectrum from "pure" unit tests through to fully integrated systems tests. We've described low level unit tests above. Integrated testing typically involves some sort of script that simulates user actions and then verifies that the result matches what's expected. This sort of "end to end" test verifies that all parts of the system are working correctly.
It's unfortunate that there is no clear nomenclature to describe all the intermediate stages of testing. The next stage beyond testing a single unit of code is subsystem testing. A subsystem test verifies that two or more units of code are interacting correctly to produce the desired result. In the simplest case, a subsystem test can be created simply by replacing mock objects with real objects and running unit tests on the top level module. In practise, this tends to not work as well as expected, because the original unit test data wasn't designed for a subsystem test, or because the nature of the test cases needs to be changed in order to fully test the subsystem. After all there is little point in simply repeating the unit test cases; the objective of a subsystem test should be to test boundary conditions and special cases that would be difficult to duplicate in unit tests.
Once a subsystem has been tested, it can be integrated into a larger system, which is still a subset of the whole product. Tests can be written for larger and larger subsystems, but at each stage the complexity of the tests increases. At some point, the effort required to hand craft tests exceeds the benefits of running them. This is where integrated testing comes in.
Integrated testing involves recording a user's interaction with the system into a script that can be replayed. The testing framework then compares the system's response with the expected response and passes or fails the test. The PHPUnit testing framework that we use has the ability to work with Selenium, a browser based test automation tool. Writing a functional test using Selenium is documented here.
The purpose of unit tests is to isolate a module of code. A test that tests only one thing provides better information than a test that involves several object interactions. But how do we isolate an object from its dependencies? By writing stub classes. xUnit Patterns defines a the hierarchy of dummy classes, ranging from simple to complex:
Unit testing capabilities in Joomla are steadily developing. [Add note re amount of coverage for platform by unit tests.]
If you can commit to the Joomla code base, then you should consider yourself part of the unit test team!
Writing tests concurrently with code (or even before) is a good way to not only save development time, but a great tool for defending against regressions. Writing tests early in the development cycle also helps identify and resolve design issues sooner, which reduces refactoring.
If you want to get started on unit testing, get in touch with Alan Langford (instance) or Ray Tsai (mihu). Either of us will be happy to help out.
At risk of stating the obvious, in the "purest" case the purpose of a unit test is to isolate a unit of code from its environment and to test the operation of that code.
This isolation is usually achieved by writing dummy classes that emulate the code unit's environment. These dummy objects can be passive, by simply simulating the environment, or they can be more active, keeping track of how they are being used by the test unit and reporting any variations from the expected behaviour. See Mock Objects in Joomla for a detailed example.
An interesting aspect of writing tests is that they become de facto detailed technical specifications of the interfaces between units of code. The fact that these specifications can be verified in an automated way makes them a superb resource when refactoring code.
The test code has a few templates designed to kick-start a test. They are:
Test files follow the form classnameTest.php, for example JObjectTest.php. For tests that are not class based, use the name of the file being tested.
Joomla unit tests use the standard PHPUnit test runner. See http://www.phpunit.de for documentation.
Before you start make sure you have installed PHPUnit and of course PHP (5!) properly...
To get the unit tests to run on your Joomla! installation, perform the following steps:
The unit test will the run, and the results are rendered. You will see a series of dots for each passed test and other letters for failed tests.
See http://www.phpunit.de/manual/current/en/textui.html for help using the—filter switch to run only certain tests. There are also many other command line switches you can use to get results in various formats.
The provided configurations should work out of the box. We have seen problems with it (currently the cause is unknown). If you get an error like below, the solution is pretty easy.
file=/var/www/unittest/runtests.php posn=17 base=runtests.php /var/www JPATH_BASE does not point to a valid Joomla! installation: JPATH_BASE = /var/www Please modify your copy of "TestConfiguration.php"
Modify the "TestConfiguration.php" file and change the definition of the JPATH_BASE so it points to the path of you Joomla! installation, in the example below the Joomla! installation is installed at "/var/www/update".
Why can't I use "phpunit testname.php" to run my tests?
The test facility has to do some work to be able to load the "Joomla!" framework and to be able to inject mock classes. It's difficult to do this from the PHPUnit test runner, so we built our own. Also, the Joomla test runner has specific options designed to make it easy to select specific tests. Over time we will add more functionality to the test runner so it has many of the capabilities of the phpunit command.