Java code coverage reports in Eclipse

A part of our team’s “definition of done” is having unit-tests in place and, unofficially, a minimum of 80% code coverage. Our Maven-based build process runs the tests and then creates code coverage reports in HTML format, that we can then consult in the documentation that Maven generates. Along with other reports, this helps us get a clear picture of where our code is in terms of stability and quality.

This is all great ; but when you’re in the middle of a task and you write unit-tests, it’s quite tedious to run the build and then open the HTML coverage report just to monitor your code coverage. I spend about 80% of my time for a task in Eclipse : opening and activating tasks with Mylyn, coding, writing unit-tests, running unit-tests and so on. This is why for me it made sense to seek out a way to monitor the code coverage in Eclipse.

After a bit of googling, I found a Java code coverage plug-in for Eclipse : EclEmma. As you can see from its name, it’s based on the EMMA Java code coverage tool. Here’s a list with its main features :

• a coverage mode in which applications launched or unit tests are instrumented and measured
• coverage overview : a coverage view containing a report on the source code coverage values at project-level, package-level and class-level
• source highlighting in the Java code editor using customizable colors
• customizable coverage counters
• multiple coverage sessions and session merging
• importing EMMA coverage data files
• exporting to EMMA coverage data, XML and HTML

The easiest way to install it is through the update site : http://update.eclemma.org. After the installation, you will notice a new launch mode appearing in the Eclipse toolbar, called Coverage, similar to the Run and Debug modes. This new mode allows you to run coverage reports on applications or unit-tests just like you would before run those applications or unit-tests.

In a project I’m currently working on, our server-side unit tests are written using TestNG. From Eclipse, I can run one or multiple TestNG units using the Eclipse TestNG plug-in, so I can easily verify that my code passes the unit tests. I have defined a launch configuration for each server-side project which runs all of the unit-tests. To check out the code coverage for those tests, all I have to do is create a coverage configuration and make sure that I select the source code folders to be instrumented.

I created a sample Java-Maven-TestNG project and added to it a simple class called ShoppingCartImpl along with a TestNG test class. Here’s how it looks :

Source code of a very basic shopping cart

As you can see, this is a very basic class. Now on to configuring the coverage settings ; this is a simple matter of clicking on the Coverage button in Eclipse’s toolbar and selecting the menu option Coverage Configurations…. This opens up the coverage configuration window, as seen below :

Creating a new EclEmma coverage configuration

All I have to do is select the TestNG test suite that I want to run and check the source folders that are relevant to code coverage. I’m using Maven and all my source code is in src/main/java so I only select that folder. I click Apply and then I can finally run the coverage report. I click on the Coverage button and theTestNG configuration is executed and the coverage report is available :

Code coverage report after a first run

In the bottom of the Eclipse window, you get a clear picture of the code coverage. As you can see, the are reports at project, package and class level, which also show up in the package explorer, in the left. To enable the decorators in the package explorer, go to the Eclipse menu and select Preferences -> General -> Appearance -> Label decorations, then make sure that the Java Code Coverage label decoration option is checked.

Another interesting feature of EclEmma is that after the code coverage instrumentation you can actually see the coverage in the source code. As you can see, each line relevant to the coverage report is marked with a color. Green is for 100% branch coverage, yellow is for some branch coverage and red for no coverage at all. The shopping cart has quite a low code coverage so I did shape it up. After a bit of fiddling with the code, I get a 100% code coverage and a very nice report :

The ShoppingCart class with 100% code coverage