How to Measure JaCoCo Code Coverage in a Multi-Module Maven Project?

How can I implement JaCoCo to measure code coverage in a Maven multi-module project?

<dependency>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.7</version>
</dependency>

JaCoCo is a popular Java code coverage tool that integrates seamlessly with Maven, making it an excellent choice for multi-module projects. This guide provides step-by-step instructions on setting up JaCoCo in a Maven multi-module environment.

<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.7</version>
    <executions>
        <execution>
            <goals>
                <goal>prepare-agent</goal>
            </goals>
        </execution>
        <execution>
            <id>report</id>
            <phase>test</phase>
            <goals>
                <goal>report</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Causes

• Incorrect plugin configuration in the parent POM
• Missing configuration in module POM files
• Dependency issues between modules

Solutions

• Add the JaCoCo Maven plugin to the parent POM's build section
• Configure each module to inherit the JaCoCo settings from the parent POM
• Ensure all required dependencies are included in each module's POM

Mistake: Not including JaCoCo plugin in the parent POM.

Solution: Ensure the JaCoCo Maven plugin is added in the parent POM's dependencies.

Mistake: Failing to bind the JaCoCo report generation to the test phase.

Solution: Add the correct execution phase for report generation.

Mistake: Issues with module dependencies preventing accurate coverage reports.

Solution: Check and resolve transitive dependencies between modules.