Jacoco

Jacoco is an open-source code coverage tool for Java applications designed to measure and report how much of a program's source code is executed during testing. Developed by the Eclipse Foundation, Jacoco provides detailed insights into which parts of the codebase are covered by tests, helping developers identify untested or poorly tested areas.

The tool works by instrumenting Java bytecode, adding probes to track which methods and branches are executed during test runs. This instrumentation is typically performed during the build process, allowing developers to analyze coverage without modifying their source code. Jacoco supports various testing frameworks, including JUnit, TestNG, and Spock, and integrates seamlessly with build tools like Maven and Gradle.

Key features of Jacoco include the ability to generate HTML, XML, or text reports, visualize coverage in a browser, and filter results by package or class. It also supports advanced metrics such as line, branch, and instruction coverage, providing a comprehensive view of test effectiveness. Jacoco’s lightweight design ensures minimal performance overhead, making it suitable for large-scale applications.

The tool is widely used in continuous integration (CI) pipelines to enforce coverage thresholds, ensuring that new code changes maintain or improve test coverage. Its flexibility and integration capabilities make it a popular choice for teams adopting test-driven development (TDD) or behavior-driven development (BDD) practices. Jacoco is released under the Eclipse Public License (EPL), ensuring free and open access to its features.