In this tutorial I’ll show how to use Jacoco with Maven/Tycho to create a code coverage report of multiple Eclipse plug-in projects.

The code of the example is available here: https://github.com/LorenzoBettini/tycho-multiproject-jacoco-report-example.

This is the structure of the projects:

Each project’s code is tested in a specific .tests project. The code consists of simple Java classes doing nothing interesting, and tests just call that code.

The Maven parent pom file is written such that Jacoco is enabled only when the profile “jacoco” is explicitly activated:

This is just an example of configuration; you might want to tweak it as you see fit for your own projects (in this example I also created a Main.java with a main method that I exclude from the coverage). By default, the jacoco-maven-plugin will “prepare” the Jacoco agent in the property tycho.testArgLine (since our test projects are Maven projects with packaging eclipse-plugin-test); since tycho.testArgLine is automatically used by the tycho-surefire-plugin and since we have no special test configuration, the pom.xml of our test projects is just as simple as this:

if you need a custom configuration, then you have to explicitly mention ${tycho.testArgLine} in the <argLine>.

Now we want to create an aggregate Jacoco report for the classes in plugin1 and plugin2 projects (tested by plugin1.tests and plugin2.tests, respectively); each test project will generate a jacoco.exec file with coverage information. Before Jacoco 0.7.7, creating an aggregate report wasn’t that easy and required to store all coverage data in a single an .exec file and then use an ant task (with a manual configuration specifying all the source file and class file paths). In 0.7.7, the jacoco:report-aggregate has been added, which makes creating a report really easy!

Here’s an excerpt of the documentation:

So it’s just a matter of creating a separate project (I called that example.tests.report) where we:

• configure the report-aggregate goal (in this example I bind that to the verify phase)
• add as dependencies with scope compile the projects containing the actual code and with scope test the projects containing the tests and .exec data

That’s all!

Now run this command in the example.parent project:

and when the build terminates, you’ll find the HTML code coverage report for all your projects in the directory (again, you can configure jacoco with a different output path, that’s just the default):

/example.tests.report/target/site/jacoco-aggregate

Since, besides the HTML report, jacoco will create an XML report, you can use any tool that keeps track of code coverage, like the online free solution Coveralls (https://coveralls.io/). Coveralls is automatically accessible from Travis (I assume that you know how to connect your github projects to Travis and Coveralls). So we just need to configure the coveralls-maven-plugin with the path of the Jacoco xml report (I’m doing this in the parent pom, in the pluginManagement section in the jacoco profile):

And here’s the Travis file:

This is the coveralls page for the example project https://coveralls.io/github/LorenzoBettini/tycho-multiproject-jacoco-report-example. And an example of coverage information:

That’s all!

Happy coverage! 🙂