Introduction :#

JaCoCo Test Report Generation provides insights into your test coverage by analyzing which parts of your code are executed during testing. It involves instrumenting your code, collecting coverage data during test runs, and generating detailed reports. These reports help identify untested code areas, guiding improvements in test coverage and overall code quality. JaCoCo integrates with build tools like Maven and Gradle for easy inclusion in continuous integration processes.

Test Report Generation with JaCoCo involves several key steps:

1. Instrumentation: JaCoCo instruments the bytecode of your classes, either at runtime or during build time, to collect coverage data as your tests execute.
2. Execution: As your tests run, JaCoCo collects coverage metrics, including information on which lines of code were executed and which were not.
3. Report Creation: After test execution, JaCoCo generates detailed reports that provide insights into code coverage. These reports typically include metrics such as line coverage, branch coverage, and method coverage.
4. Analysis: The generated reports can be used to identify gaps in test coverage and guide the development of additional tests. They help ensure that your application is thoroughly tested and that critical code paths are covered.

JaCoCo - Java Code Coverage#

JaCoCo is a free Java code coverage library distributed under the Eclipse Public License. It is commonly used in Java projects to measure the effectiveness of unit and integration tests by providing coverage metrics. To integrate JaCoCo with Maven, you can use the JaCoCo Maven plugin, which automates the process of collecting coverage data during test execution.

When running tests with JUnit, the JaCoCo agent is automatically triggered. This agent collects coverage information and generates a coverage report in binary format, stored in the target directory as target/jacoco.exec. For detailed instructions on setting up the JaCoCo Maven plugin, you can refer to the plugin documentation https://www.baeldung.com/jacoco .

Go to that link, and after scrolling down, you will see the Maven configuration. Just copy these dependencies and add them to the Maven configuration section(inside the ‘plugin’ section) of your pom.xml file.

Go to jacoco-maven-plugin Maven Repository: org.jacoco » jacoco-maven-plugin and check what the latest version is. Then, add that version to your jacoco-maven-plugin configuration.

Here, we add Maven Repository: org.jacoco » jacoco-maven-plugin » 0.8.12 version.

		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
			<plugin>
				<groupId>org.jacoco</groupId>
				<artifactId>jacoco-maven-plugin</artifactId>
				<version>0.8.12</version>
				<executions>
					<execution>
						<goals>
							<goal>prepare-agent</goal>
						</goals>
					</execution>
					<execution>
						<id>report</id>
						<phase>prepare-package</phase>
						<goals>
							<goal>report</goal>
						</goals>
					</execution>
				</executions>
			</plugin>

		</plugins>

After adding these plugins you have to reload maven.

Run Maven Commands#

After adding the necessary JaCoCo dependencies and configuring the JaCoCo Maven plugin in your pom.xml, running mvn package will automatically trigger the generation of code coverage reports.

Execute the command mvn package. During this process, Maven will:

• Compile your code and run your tests.
• JaCoCo’s agent will instrument the bytecode to collect coverage data.
• Generate the coverage data file (jacoco.exec).
• Create the JaCoCo coverage report in the specified format (e.g., HTML, XML) and place it in the target directory.

After the Maven build completes, you can find the JaCoCo reports in the target/site/jacoco directory (for HTML reports) or as specified in your configuration. Open the index.html file in a web browser to view the coverage report.

To run Maven commands like mvn package, you typically use the terminal or command line interface of your IDE.

• Enter the right directory write cd <your directory name>
• If maven is installed in your system then write mvn clean package
• If Maven is Not Installed (Using Wrapper):
  • write ./mvnw clean package (For mac)
  • write .\mvnw.cmd clean package (For windows)

After running the Maven command (like mvn clean package), you should find a jacoco.exec file inside the target directory of your project.

If you go to target/site/jacoco/ directory, you can see the ‘index.html’ file you can open this file using any of yours browser.

When you open the index.html file from the JaCoCo report, you’ll see a detailed HTML page that summarizes your code coverage. Here’s what you can typically find on that page:

1. Coverage Summary
2. Package and Class Listings
3. Detailed Class Coverage
4. Coverage Breakdown by Method
5. Navigational Links

Using the Report:#

• Identify Uncovered Code: Focus on the red lines to see which parts of your code need more test cases.
• Refine Test Cases: Use the insights gained to refine and improve your unit and integration tests.
• Monitor Code Quality: Regularly check the coverage report to ensure new changes are covered by tests.

This comprehensive overview allows you to ensure your application is well-tested and helps maintain high code quality.

Benefits of JaCoCo#

• Visibility into Test Coverage: JaCoCo provides clear metrics on how much of your code is tested, offering a comprehensive view of your test coverage. This visibility helps ensure that your tests are covering the intended parts of your application.
• Identify Dead Code: By highlighting code that is not executed during tests, JaCoCo helps identify "dead code"—parts of the codebase that are not used. This allows for cleaner and more maintainable code by removing or refactoring unused code.
• Focus on Critical Areas: JaCoCo shows which parts of your code are not covered by tests, enabling you to direct your testing efforts toward the most critical and potentially vulnerable areas of your application. This targeted approach helps improve the overall reliability and robustness of your software.
• Better Project Maintenance, Compliance, and Standards: Regular use of JaCoCo helps maintain high code quality standards and compliance with testing requirements. By ensuring comprehensive test coverage, JaCoCo contributes to better project maintenance and adherence to coding and testing standards.