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Analysis and Strategy for JaCoCo Coverage with Python Integration Tests

Current Situation Analysis

You’ve set up a multi-module Maven project with:

Your goal is to use Python’s unittest to test API endpoints and generate coverage reports for the Java code. The challenge is that Python tests live outside the Java project, and you need to run Jetty to serve the application during testing.

Problems with the Current Approach

  1. Multiple Runs Issue: You’re running PlaygroundWeb multiple times to generate separate coverage reports for different modules, which is inefficient.

  2. Scalability Concern: This approach won’t scale well with more modules. For a project with 10 modules, you’d need 10 separate runs.

  3. Coverage Fragmentation: Per-module reports make it harder to get a holistic view of coverage across the entire application.

1. Consolidated Coverage Collection Approach

Instead of running the application multiple times, I recommend:

  1. Run the web application once with JaCoCo agent attached
  2. Execute all Python integration tests against this single instance
  3. Generate a consolidated coverage report that includes all modules

This approach is more efficient and provides a unified view of coverage across your entire application.

2. Implementation Steps

Parent POM (PlaygroundLib) Modifications

Add a profile for integration testing with JaCoCo:

<profiles>
    <profile>
        <id>integration-test</id>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.jacoco</groupId>
                    <artifactId>jacoco-maven-plugin</artifactId>
                    <executions>
                        <execution>
                            <id>merge</id>
                            <phase>post-integration-test</phase>
                            <goals>
                                <goal>merge</goal>
                            </goals>
                            <configuration>
                                <fileSets>
                                    <fileSet>
                                        <directory>${project.basedir}</directory>
                                        <includes>
                                            <include>*/target/jacoco-it.exec</include>
                                        </includes>
                                    </fileSet>
                                </fileSets>
                                <destFile>${project.build.directory}/jacoco-merged.exec</destFile>
                            </configuration>
                        </execution>
                        <execution>
                            <id>report-merged</id>
                            <phase>verify</phase>
                            <goals>
                                <goal>report</goal>
                            </goals>
                            <configuration>
                                <dataFile>${project.build.directory}/jacoco-merged.exec</dataFile>
                                <outputDirectory>${project.reporting.outputDirectory}/jacoco-merged</outputDirectory>
                            </configuration>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>
    </profile>
</profiles>

PlaygroundWeb POM Modifications

Modify the JaCoCo agent configuration to include all modules:

<plugin>
    <groupId>org.eclipse.jetty</groupId>
    <artifactId>jetty-maven-plugin</artifactId>
    <executions>
        <execution>
            <id>start-jetty</id>
            <phase>pre-integration-test</phase>
            <goals>
                <goal>start</goal>
            </goals>
            <configuration>
                <daemon>true</daemon>
                <jvmArgs>
                    -javaagent:${settings.localRepository}/org/jacoco/org.jacoco.agent/${jacoco.version}/org.jacoco.agent-${jacoco.version}-runtime.jar=destfile=${project.build.directory}/jacoco-it.exec,includes=org.lzw.*
                </jvmArgs>
                <!-- Rest of configuration remains the same -->
            </configuration>
        </execution>
        <!-- Rest of executions remain the same -->
    </executions>
</plugin>

Note the addition of includes=org.lzw.* in the JaCoCo agent configuration. This ensures that all classes in the org.lzw package (across all modules) are included in the coverage report.

3. Execution Flow

The recommended execution flow would be:

# Build all modules
mvn clean install

# Run integration tests with coverage
mvn verify -Pintegration-test

This will:

  1. Compile all modules
  2. Start Jetty with JaCoCo agent attached
  3. Run Python integration tests
  4. Stop Jetty
  5. Generate a merged coverage report for all modules

4. Scaling to Larger Projects

For a larger project with ten modules:

  1. Web modules (like PlaygroundWeb) would be configured to run the application with JaCoCo agent attached.
  2. Utility modules (like PlaygroundUtils) would not need special configuration.
  3. The parent POM would handle merging coverage data from all modules.

If you have multiple web modules that need to be tested independently, you could create separate Maven profiles for each web module and run integration tests for each separately, then merge all coverage data at the parent level.

5. Addressing JaCoCo Complexity

To manage JaCoCo’s complexity:

  1. Encapsulate configuration in Maven profiles to keep the main POM clean
  2. Document the process clearly so team members understand how to run tests and generate reports
  3. Consider CI/CD automation to reduce manual complexity for developers

Summary

The recommended approach consolidates coverage collection by running the web application once with JaCoCo agent attached, executing all Python integration tests against this instance, and generating a consolidated coverage report. This approach is more efficient, scalable, and provides a unified view of coverage across your entire application.

This strategy should solve your current challenges and scale well as your project grows, while also simplifying the management of JaCoCo’s complexity.

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