Hey guys! Ever wrestled with Jacoco and found your code coverage reports cluttered with a bunch of generated code you didn't even write? Annoying, right? This article is your friendly guide to mastering Jacoco and ensuring your reports focus on what truly matters: your hand-crafted, tested code. We'll dive deep into how to exclude generated sources, keeping your coverage reports clean, accurate, and a joy to read. Let's get started!

Why Exclude Generated Code in Jacoco?

So, why bother excluding generated code in the first place? Well, imagine this: you're diligently writing tests, striving for that sweet 100% code coverage. You run Jacoco, and… boom! Your coverage numbers are lower than expected because generated code, code that's automatically created by tools like JPA or Protobuf, is pulling them down. You might be wondering, what's wrong with the code generation? The truth is, that generated code isn't typically written by you. It's often boilerplate or implementation details that your tests probably don't need to cover. The primary goals of these tests should be to check the functionality of your own code, so that is the main reason why you want to exclude generated sources.

• Focus on Relevant Coverage: The most important reason is to focus your coverage reports on the code you've actually written and are responsible for. It helps you quickly identify gaps in your testing of core logic, rather than getting bogged down in generated methods. You can also quickly find the most important parts of the code.
• Improve Readability: Excluded generated code results in a cleaner coverage report. It's easier to scan the report and pinpoint areas needing more testing when you're not distracted by hundreds of lines of autogenerated code.
• Avoid Unnecessary Test Maintenance: You don't want to waste time writing tests for code you didn't write. Generated code can change due to updates in the tools that create it. Writing tests for it will result in more maintenance overhead.
• Accurate Metric Measurement: Including generated code can skew your coverage metrics. This can make it seem like you have less code covered than you actually do, potentially leading to incorrect assumptions about your project's quality.

Ultimately, excluding generated code makes your coverage reports more insightful and actionable, helping you build better software. Now, let's look at the methods for excluding your files!

Methods for Excluding Generated Code in Jacoco

Alright, let's get into the nitty-gritty of excluding generated code. Jacoco offers a few different ways to accomplish this, and the best approach often depends on how your code is generated and how your project is structured. These options can be set up in your build.gradle or pom.xml file, depending on whether you're using Gradle or Maven, respectively.

1. Using @Generated Annotation

This is often the easiest and most effective method if your code generation tools add the @Generated annotation from javax.annotation.Generated. Jacoco can be configured to automatically exclude classes marked with this annotation. The @Generated annotation is a standard way to mark code that has been automatically generated, making it easy to identify and exclude such code during coverage analysis. Let's say, your code generator uses @Generated annotation, the corresponding configuration in your build file will be pretty straight forward. However, if your generator doesn't use the @Generated annotation, then the following options are probably useful.

Gradle Example

jacoco {
    toolVersion = "0.8.11"
    excludes = ["**/gen/**", "**/Generated*.class"]
}

task jacocoTestReport(type: org.gradle.testing.jacoco.tasks.JacocoReport) {
    group = "Reporting"
    dependsOn test
    executionData fileTree(project.buildDir).include("**/jacoco/test.exec")

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

    classDirectories.setFrom(files(classDirectories.files.collect { dir ->
        fileTree(dir) {
            exclude '**/gen/**'
            exclude '**/Generated*.class'
            exclude '**/com/example/generated/*'
        }
    }))
}

Maven Example

<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.11</version>
    <executions>
        <execution>
            <goals>
                <goal>prepare-agent</goal>
            </goals>
        </execution>
        <execution>
            <id>report</id>
            <phase>test</phase>
            <goals>
                <goal>report</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <excludes>
            <exclude>**/gen/*</exclude>
            <exclude>**/Generated*</exclude>
            <exclude>**/com/example/generated/*</exclude>
        </excludes>
    </configuration>
</plugin>

2. Excluding by Package or Class Name

If your generated code is consistently in a specific package or follows a naming convention, you can exclude it using wildcards. This approach is generally pretty useful, if you can control where the sources are generated. The exclusions are configured in your build file. This method is handy when you have a well-defined structure for your generated code.

Gradle Example

jacoco {
    toolVersion = "0.8.11"
    excludes = ["**/gen/**", "**/Generated*.class"]
}

task jacocoTestReport(type: org.gradle.testing.jacoco.tasks.JacocoReport) {
    group = "Reporting"
    dependsOn test
    executionData fileTree(project.buildDir).include("**/jacoco/test.exec")

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

    classDirectories.setFrom(files(classDirectories.files.collect { dir ->
        fileTree(dir) {
            exclude '**/gen/**'
            exclude '**/Generated*.class'
            exclude '**/com/example/generated/*'
        }
    }))
}

Maven Example

<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.11</version>
    <executions>
        <execution>
            <goals>
                <goal>prepare-agent</goal>
            </goals>
        </execution>
        <execution>
            <id>report</id>
            <phase>test</phase>
            <goals>
                <goal>report</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <excludes>
            <exclude>**/gen/*</exclude>
            <exclude>**/Generated*</exclude>
            <exclude>**/com/example/generated/*</exclude>
        </excludes>
    </configuration>
</plugin>

3. Combining Methods

For more complex scenarios, you can combine these methods. For instance, you could use package exclusions in combination with @Generated to catch any edge cases that might slip through. The combination of techniques ensures you have the most robust and accurate coverage reports.

Troubleshooting Jacoco Exclusions

Alright, so you've set up your exclusions, but your reports still look a bit… off? Don't worry, it happens! Here's how to troubleshoot common issues:

• Verify Configuration: Double-check your build.gradle or pom.xml files for typos or incorrect path patterns. A simple mistake can render your exclusions ineffective. Review the file paths and patterns to ensure they accurately reflect the location and naming of your generated code. For instance, a typo in a package name can prevent the exclusion from working.
• Clean and Rebuild: Sometimes, Gradle or Maven can cache old builds. Run a clean build to ensure the latest configurations are applied. This will force Jacoco to re-analyze your code and apply the exclusions. Make sure you clear out any build artifacts, then rebuild.
• Check Generated Code Location: Make sure you have correctly identified the location of your generated code. Generated code can be stored in unexpected locations. Verify that your exclusion patterns are correctly targeting the directory or package where the generated files reside. Confirm that the path in your exclusion matches the actual file structure.
• Use Detailed Reports: Generate detailed reports (e.g., HTML reports) to examine the coverage of specific classes and packages. This helps you pinpoint whether your exclusions are working correctly. Inspect the HTML reports to see which files are being included and excluded from the coverage analysis. You can quickly see whether the generated files are still showing up in the coverage results.
• Incremental Builds: If you're using incremental builds, ensure that your exclusions are applied correctly during incremental builds. Sometimes, changes in exclusions may not be fully reflected without a full clean build. In complex projects, incremental builds can sometimes lead to unexpected results. Performing a full build can help resolve inconsistencies.

Best Practices for Jacoco Exclusions

Let's wrap things up with some best practices to keep in mind when excluding generated code:

• Be Specific: Avoid overly broad exclusions. Only exclude what's truly generated. Overly broad exclusion patterns might unintentionally exclude relevant code.
• Test Your Configuration: After setting up exclusions, run a test to verify the coverage report shows what you expect. Run your tests and review the coverage report to ensure the generated code is excluded. Make sure your coverage numbers are accurate and reflect only the code you've written.
• Document Your Exclusions: Explain why you're excluding certain code in a comment in your build file. This helps others understand your project's configuration. Documenting your exclusion strategies is important for maintainability.
• Regularly Review: Periodically review your exclusions to ensure they remain relevant as your project evolves. Your project and build setup might change, so it's good to keep an eye on them.

Conclusion

So there you have it, guys! You now have a solid understanding of how to exclude generated code in Jacoco. By following these steps, you can ensure your code coverage reports provide accurate and meaningful insights into your project's test quality. Remember to prioritize your own code and keep those reports clean. Happy coding, and keep those coverage percentages high! Hopefully, this article helps to remove the pain when you have to use Jacoco. If you have any questions, feel free to ask!