Understanding JaCoCo and Gradle

Oct 13, 2025 by talynt.org 65 views

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Introduction

In Android projects, especially those with multiple modules, generating a single Jacoco code coverage report can be a challenging task. The Android Gradle Plugin and JaCoCo provide a robust way to generate code coverage reports, but it requires careful configuration to achieve a single report for the entire project. In this article, we will explore how to configure JaCoCo to generate a single code coverage report for a multi-module Android project.

Understanding JaCoCo and Gradle

What is JaCoCo?

JaCoCo is a free, open-source tool for measuring code coverage of Java applications. It provides detailed information about the code coverage, including the number of lines, methods, and branches executed during testing. JaCoCo is widely used in the Android community to generate code coverage reports.

What is Gradle?

Gradle is a build tool for automating the build, test, and deployment process of software projects. It provides a flexible and powerful way to manage dependencies, build configurations, and tasks. In Android projects, Gradle is used to manage the build process, including the generation of code coverage reports using JaCoCo.

Configuring JaCoCo for Multi-Module Projects

To generate a single code coverage report for a multi-module project, we need to configure JaCoCo to aggregate the coverage data from all modules. Here's an example of how to configure JaCoCo in the jacoco.gradle file:

apply plugin: 'jacoco'

def coverageSourceDirs = [
    project(':module1').sourceSets.main.java.srcDirs,
    project(':module2').sourceSets.main.java.srcDirs,
    // Add more modules as needed
]

jacoco {
    toolVersion = '0.8.7'
    reports {
        xml.enabled = true
        csv.enabled = true
        html.enabled = true
    }
    classDirectories {
        include '**/*.class'
    }
    sourceDirectories {
        include files(coverageSourceDirs)
    }
}

In this example, we define a list of source directories for each module using the coverageSourceDirs variable. We then configure JaCoCo to include these source directories in the coverage report.

Aggregating Coverage Data

To aggregate the coverage data from all modules, we need to configure Gradle to run the JaCoCo task for each module and then aggregate the results. Here's an example of how to configure Gradle to aggregate the coverage data:

task jacocoAggregate(type: JacocoReport) {
    group = 'Reporting'
    description = 'Generate Jacoco code coverage report'

    sourceDirectories = files(coverageSourceDirs)
    classDirectories = files(fileTree(dir: project(':module1').buildDir, include: 'classes/java/main'), fileTree(dir: project(':module2').buildDir, include: 'classes/java/main'), // Add more modules as needed)

    executionData = files(fileTree(dir: project(':module1').buildDir, include: 'jacoco/test.exec'), fileTree(dir: project(':module2').buildDir, include: 'jacoco/test.exec'), // Add more modules as needed)

    reports {
        xml.enabled = true
        csv.enabled = true
        html.enabled = true
    }
}

In this example, we define a new task called jacocoAggregate that runs the JaCoCo report task for each module and aggregates the results. We configure the task to include the source directories, class directories, and execution data for each module.

Running the JaCoCo Task

To run the JaCoCo task, we need to add the jacocoAggregate task to the assemble task. Here's an example of how to add the task:

assemble.dependsOn jacocoAggregate

This will run the jacocoAggregate task when the assemble task is executed.

Conclusion

In this article, we explored how to configure JaCoCo to generate a single code coverage report for a multi-module Android project. We discussed the importance of understanding JaCoCo and Gradle, and how to configure JaCoCo to aggregate the coverage data from all modules. We also showed how to run the JaCoCo task and aggregate the results. By following these steps, you can generate a single code coverage report for your multi-module Android project.

Example Use Case

Here's an example use case for generating a single code coverage report for a multi-module Android project:

Suppose we have a multi-module Android project with three modules: module1, module2, and module3. Each module has its own source code and test code. We want to generate a single code coverage report that includes the coverage data from all three modules.

To achieve this, we can configure JaCoCo as shown in the previous examples. We define a list of source directories for each module using the coverageSourceDirs variable. We then configure JaCoCo to include these source directories in the coverage report.

We also configure Gradle to run the JaCoCo task for each module and aggregate the results. We define a new task called jacocoAggregate that runs the JaCoCo report task for each module and aggregates the results.

Finally, we add the jacocoAggregate task to the assemble task, so that it runs when the assemble task is executed.

By following these steps, we can generate a single code coverage report that includes the coverage data from all three modules.

Best Practices

Here are some best practices to keep in mind when generating a single code coverage report for a multi-module Android project:

Use a consistent naming convention for the source directories and class directories.
Use a consistent naming convention for the execution data files.
Make sure to include all modules in the coverage report.
Use a single task to aggregate the coverage data from all modules.
Use a single report file to store the aggregated coverage data.

By following these best practices, you can ensure that your code coverage report is accurate and comprehensive.

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Q: What is the purpose of using JaCoCo in Android projects?

A: JaCoCo is a free, open-source tool for measuring code coverage of Java applications. It provides detailed information about the code coverage, including the number of lines, methods, and branches executed during testing. JaCoCo is widely used in the Android community to generate code coverage reports.

Q: How do I configure JaCoCo to generate a single code coverage report for a multi-module project?

A: To configure JaCoCo to generate a single code coverage report for a multi-module project, you need to define a list of source directories for each module using the coverageSourceDirs variable. You then configure JaCoCo to include these source directories in the coverage report. Additionally, you need to configure Gradle to run the JaCoCo task for each module and aggregate the results.

Q: What is the difference between the `jacoco` task and the `jacocoAggregate` task?

A: The jacoco task is used to generate the code coverage report for a single module, while the jacocoAggregate task is used to aggregate the code coverage data from multiple modules.

Q: How do I add the `jacocoAggregate` task to the `assemble` task?

A: To add the jacocoAggregate task to the assemble task, you need to add the following line to your build.gradle file:

assemble.dependsOn jacocoAggregate

Q: What are the best practices for generating a single code coverage report for a multi-module project?

A: Here are some best practices to keep in mind when generating a single code coverage report for a multi-module project:

Use a consistent naming convention for the source directories and class directories.
Use a consistent naming convention for the execution data files.
Make sure to include all modules in the coverage report.
Use a single task to aggregate the coverage data from all modules.
Use a single report file to store the aggregated coverage data.

Q: How do I troubleshoot issues with the JaCoCo report?

A: Here are some steps you can take to troubleshoot issues with the JaCoCo report:

Check the Gradle build output for any errors or warnings.
Verify that the coverageSourceDirs variable is correctly defined.
Check that the jacoco task is correctly configured for each module.
Verify that the jacocoAggregate task is correctly configured to aggregate the coverage data from all modules.

Q: Can I use JaCoCo with other build tools, such as Maven?

A: Yes, JaCoCo can be used with other build tools, such as Maven. However, the configuration may vary depending on the build tool and the project structure.

Q: How do I customize the JaCoCo report?

A: You can customize the JaCoCo report by modifying the jacoco task configuration. For example, you can change the report format, add custom metrics, or modify the report layout.

Q: Can I use JaCoCo with Android Studio?

A: Yes, JaCoCo can be used with Android Studio. You can configure JaCoCo in the build.gradle file and then run the JaCoCo task from the Android Studio UI.

Q: How do I integrate JaCoCo with other tools, such as SonarQube?

A: You can integrate JaCoCo with other tools, such as SonarQube, by configuring the JaCoCo task to generate a report in a format that can be consumed by the other tool. For example, you can configure JaCoCo to generate a CSV report that can be imported into SonarQube.