Getting code coverage in the Play Framework using Jacoco

QUICKLINK: I don’t care about your stupid life story, just show me how to make it work

We’ve been using the Play framework lately at KonciergeMD to build our application. One thing that’s always good to have on your application is good test coverage, and there’s no shortage of tools to measure that.

To get the reports on code coverage, we decided to give JaCoCo a shot, and specifically try to use the sbt-jacoco plugin to do it.

Trying to use it right out of the box, however, proved useless. Running jacoco:cover from sbt or play would not work, and instead run no tests while not giving any error messages, and making you feel like a fool for trying.

After staring at the problem for a while, @seantbrady and I finally came across the solution. The main and simple issue with it is that sbt runs tests in parallel by default, and this is what the sbt-jacoco plugin inherits. You can see this by doing the following in the play console:

[webapp] $ jacoco:parallel-execution
[info] true

Play, however, has this set to false. The simple solution, then, is to set this to false for jacoco also.

How to make it work

UPDATE: We originally had the settings in a separate build.sbt file in the root directory to make this work. A quick email from Peter Hausel at Typesafe showed us how we can do it in the Build.scala file present in the project directory.

Some of this is covered in the sbt-jacoco wiki, but I’m going to put it all here for completeness.

• Add the following to the plugins.sbt

libraryDependencies ++= Seq(
	"org.jacoco" % "org.jacoco.core" % "0.5.7.201204190339" artifacts(Artifact("org.jacoco.core", "jar", "jar")),
	"org.jacoco" % "org.jacoco.report" % "0.5.7.201204190339" artifacts(Artifact("org.jacoco.report", "jar", "jar")))

addSbtPlugin("de.johoop" % "jacoco4sbt" % "1.2.2")

• We also added the following to the Build.scala file in the project directory

import de.johoop.jacoco4sbt.JacocoPlugin._


object ApplicationBuild extends Build {

	val appName         = "webapp"
	val appVersion      = "1.0-SNAPSHOT"

	lazy val s = Defaults.defaultSettings ++ Seq(jacoco.settings:_*)

	val appDependencies = Seq(
		// Add your project dependencies here,
	)
	
	val main = PlayProject(appName, appVersion, appDependencies, mainLang = JAVA, settings = s).settings(
		// Add your own project settings here
		parallelExecution in jacoco.Config := false
	)
}

I’ll highlight some of the more important parts of this file.

First is this line:

lazy val s = Defaults.defaultSettings ++ Seq(jacoco.settings:_*)

This adds the jacoco settings to the variable s.

Next is this line:

val main = PlayProject(appName, appVersion, appDependencies, mainLang = JAVA, settings = s).settings(

You’ll notice settings = s is added to the PlayProject. This adds the default and jacoco settings to the PlayProject.

Finally this line:

parallelExecution in jacoco.Config := false

Will make sure that parallelExecution is off during test execution.

Now you can run jacoco:cover to produce your beautiful coverage report! You can see your report at target/scala-2.9.1/jacoco/html.