jacoco's prepare-agent not generating jacoco.exec file

Question

I am running Jacoco's Maven plugin. The prepare-agent goal runs fine, but does not generate jacoco.exec file for some reason. Subsequently the report goal complains Skipping JaCoCo execution due to missing execution data file.

Any ideas?

Answer 1

Having read https://groups.google.com/forum/#!topic/jacoco/LzmCezW8VKA, it turns out that prepare-agent sets a surefire property called argLine. If you override this property (something that https://issues.apache.org/jira/browse/SUREFIRE-951 encourages you to do) then jacoco never ends up running.

The solution is to replace:

<argLine>-Dfile.encoding=${project.build.sourceEncoding}</argLine>

with

<argLine>-Dfile.encoding=${project.build.sourceEncoding} ${argLine}</argLine>

Meaning, append jacoco's argLine to the new value.

UPDATE: As pointed out by Fodder, if you aren't always running JaCoCo and no other plugin sets ${argLine} then Maven will complain that ${argLine} is undefined. To resolve this, simply define what ${argLine} should look like when JaCoCo is skipped:

<properties>
    <argLine/>
</properties>

In this case use @{argLine} instead of ${argLine} as explained here.