Code coverage in maven build - Skipping JaCoCo execution due to missing classes directory

Question

I am able to get code coverage working fine if I have a single project but now I have a multi module project.

My application is built in the api project and all my integration tests are running in a separate project which uses the artefact built as previous module.

The build runs but I dont get a code coverage report, instead I get the info message:

Skipping JaCoCo execution due to missing classes directory

My coverage report file jacoco-it.exec is created but it seems like the jacoco plugin requires the classes in the project the tests are running in.

Can somebody tell me what I need to do to be able to create a coverage report when the classes are in another module?

Answer 1

Even though jacoco:report-aggregate was meant for aggregation report on the dependencies, it did not work in my case - I use project structure like:

project
└─ module-api   ⇦ API definition
└─ module-spec  ⇦ module with black box tests through the API
└─ module-impl1 ⇦ implementation 1 of the API
└─ module-impl2 ⇦ another implementation of the API
└─ module-test1 ⇦ some dependencies + impl1, apply the tests from spec
└─ module-test2 ⇦ some dependencies + impl2, apply the tests from spec

In this case report-aggregate generated an empty report. The module-test1 and module-test2 projects are with POM packaging type, which is not suitable to run report on them too, as it requires classes in the target/classes directory.

My solution

I configured the jacoco plugin to dump the classes it instruments in the in the project's target/classes directory by adding: <classDumpDir>${project.build.outputDirectory}</classDumpDir>

This allowed the regular report goal to work. The complete code is:

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.5</version>
  <configuration>
    <destFile>${project.build.directory}/coverage-reports/code-coverage.exec</destFile>
    <dataFile>${project.build.directory}/coverage-reports/code-coverage.exec</dataFile>
    <outputDirectory>${project.reporting.outputDirectory}/code-coverage</outputDirectory>
    <propertyName>jacocoArgLine</propertyName>
    <classDumpDir>${project.build.outputDirectory}</classDumpDir>
  </configuration>
  <executions>
    <execution>
      <id>prepare-jacoco-agent</id>
      <goals>
          <goal>prepare-agent</goal>
      </goals>
    </execution>
    <execution>
      <id>post-integration-test</id>
      <phase>post-integration-test</phase>
      <goals>
        <goal>report</goal>
      </goals>
    </execution>
  </executions>
</plugin>

Please note that the instrumented classes are from all dependencies, so some filtering would be needed to narrow the report scope. See: https://www.eclemma.org/jacoco/trunk/doc/prepare-agent-mojo.html