Written by Roy van Rijn (royvanrijn.com) on
Feb 8, 2013 11:35:28
Test Swing applications in Fitnesse (Nonkey)
Fitnesse is a very popular test framework, used in a lot of projects. Using a wiki you describe the tests as plain text, which get translated into ‘fixtures’, code that is called that, in turn, can call your application. An example of a fixture we use:
The corresponding Java code could be something like:
This is a very simplified example on how you could use Fitnesse to test your application. But the idea is very powerful, there are implementations for Java (initially) and now .NET, Groovy etc. Also, most of the time the system you’re testing doesn’t have a Java API but instead you’d like to test the user interface. With most Java applications being web applications there are numerous plugins to connect Fitnesse with for example Selenium to ease web application testing. The fixtures fill webpages and analyze the resulting HTML response.
At my current client (Port of Rotterdam) we’re building a very rich, partially offline, Swing application. This application has a backend and numerous clients running the Swing application. We’ve used Fitnesse to test the backend code from the start, and the last year we’ve put in some effort to also use Fitnesse for the Swing application. We’ve called this “Nonkey”, being an automated version of our Monkey integration testing we’d been doing up to that moment.
The first ingredient we need to test Swing GUI’s in Fitnesse is UISpec4J. This is an excellent Swing test framework that allows you to manipulate GUI elements from code. The framework is made with unit-tests in mind, but can also be used in integration testing. In our SetUp page in Fitnesse we call the following code:
The WindowInterceptor captures the Swing application and allows for manipulation in a later stage. For example:
This fixture causes the Swing application to fill in the username, password and press the login button. It is easy to read and can be launched from Fitnesse with a single line:
Nice! We are done, we can test Swing GUI’s in Fitnesse now! Well no… not really, unfortunately there are a couple more problem we ran into, regaring the Event Dispatch Thread (EDT).
Event Dispatch Thread (EDT)
The EDT, sometimes called Swing Thread, is a special thread. Everything you do in Swing should always happen on this thread. Setting components to visible, pressing buttons etc, all need to be done in the EDT. If you don’t do this correctly the application gets into a lot of race conditions and it can even cause the application to hang.
When we combined Fitnesse with UISpec4J and started making a lot of tests we noticed that sometimes mysteriously a test would fail without changes. It turned out to be a problem with the EDT. UISpec4J doesn’t worry too much about the EDT, and when we click a button or setText (like the examples above) it does this in the current thread. In Fitnesse this thread is the thread that called the fixture, obviously not the EDT.
We brainstormed a lot about how we could fix this, maybe change UISpec4Js code? This turned out to be a hellish task. How about setting SwingUtilities.invokeAndWait() in every fixture? That could work but is also a massive undertaking. We decided to take a look at how Fitnesse calls the fixtures. This is always done from a ‘StatementExecutor’. So we decided to build a custom StatementExecutor which causes the fixtures to all run in the EDT.
To do this we need a custom SlimService. First I tried to extend the normal SlimService, but this wouldn’t work for some odd reason (still unexplained, should try this again). We decided to copy the SlimService code and make our own:
Next we needed a custom JavaSlimFactory:
And last but not least our custom StatementExecutor which forces all calls into the EDT thread:
This uses a small static class we’ve used in our code before to safely run a Runnable on the EDT and invokeAndWait (without waiting IN the EDT):
The only thing left to do is to instruct Fitnesse to use our SlimService instead of the default implementation. This is done using the following parameter in our main page:
Make sure that the class can be found (for example, package it in a JAR and place it on Fitnesses classpath). And you’re done! Using a ThreadCheckingRepaintManager (workings described here) we checked to see if the tests are now repainting/manipulating Swing from the correct thread, and it works like a charm.
Good luck testing with Fitnesse in the near future, if you have any problems/improvements/ideas please let me know (in the comments below).