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What is Code coverage

Code coverage is a software testing metric that measures the extent to which your codebase is tested by your test suite. It indicates the percentage of code lines, branches, or statements that have been executed during the course of running your tests. The goal of code coverage analysis is to assess the effectiveness of your testing efforts by identifying areas of code that are not being exercised by your tests.

Types of Code coverage

There are different levels of code coverage:

  1. Line Coverage: Measures the percentage of lines of code that are executed by your tests. It helps ensure that every line of code has been executed at least once.
  2. Branch Coverage: Focuses on the control flow within the code, specifically the different branches taken in conditions (e.g., if-else statements). It helps ensure that each branch is taken at least once.
  3. Statement Coverage: Similar to line coverage, but it counts individual statements within lines of code, making sure that each statement is executed.

Code coverage is an essential metric for assessing the quality of your tests and identifying areas of your codebase that might be prone to bugs due to lack of testing. However, it’s important to note that high code coverage doesn’t guarantee that your code is bug-free or that your tests cover all possible scenarios. It simply gives you a quantitative measure of how much of your code has been exercised by your test suite. It’s often used in combination with other testing metrics and practices to ensure comprehensive testing.

What percentage of code coverage is considered normal

The percentage of code coverage considered “normal” or acceptable can vary depending on the context, industry, and specific project requirements. There is no universally agreed-upon standard for what constitutes an appropriate code coverage percentage. However, I can provide some general guidelines:

  1. Minimum Threshold: Many development teams aim for a minimum code coverage percentage, often around 80% to 90%, as a starting point. This means that the test suite should cover at least 80% to 90% of the lines or statements in the codebase.
  2. Critical Components: For critical or high-risk parts of the code (such as security-sensitive areas or core business logic), teams may strive for higher code coverage percentages, often above 90% or even close to 100%.
  3. Legacy Code: Code coverage for legacy systems or code that is difficult to test may be lower, but efforts should still be made to improve coverage as much as possible while considering the practicality of testing.
  4. Balance with Other Metrics: Code coverage is just one aspect of testing quality. It’s essential to balance code coverage with other testing practices, such as unit tests, integration tests, and manual testing. A high code coverage percentage doesn’t guarantee that all scenarios are tested thoroughly.
  5. Realistic Goals: It’s crucial to set realistic goals based on the project’s resources, constraints, and specific requirements. Extremely high code coverage percentages may not be achievable or necessary for every project.
  6. Continuous Improvement: Code coverage should be seen as a tool for continuous improvement. Regularly review your code coverage, identify areas with low coverage, and work to increase coverage in those areas.

Ultimately, the “normal” or acceptable code coverage percentage will depend on factors such as project complexity, risk tolerance, testing strategy, and the quality goals of the development team. The key is to strike a balance between achieving good coverage and maintaining a practical and effective testing approach.

How to practically measure code coverage

Practically measuring code coverage involves using specialized tools that analyze the execution of your code during testing to determine which parts of the code are covered and which are not. Here’s a general step-by-step process for measuring code coverage:

  1. Choose a Code Coverage Tool: There are various code coverage tools available for different programming languages. Some popular tools include:
    • For Java: JaCoCo, Cobertura
    • For Python:, pytest-cov
    • For JavaScript: Istanbul, nyc (for Node.js)

    Choose a tool that is compatible with your programming language and testing framework.

  2. Integrate the Tool: Integrate the code coverage tool into your build and testing process. This typically involves configuring your build script or build system to use the coverage tool.
  3. Run Tests with Coverage: Execute your test suite while the code coverage tool is active. This tool will instrument your code, tracking which lines, branches, or statements are executed during the tests.
  4. Generate Coverage Reports: After running the tests, the code coverage tool generates a coverage report. This report shows which parts of your code were covered (executed) and which were not. The report may include information about line coverage, branch coverage, and other metrics.
  5. Review and Analyze Reports: Analyze the coverage reports to identify areas of the code that have low coverage. These areas may indicate code paths that are not adequately tested.
  6. Improve Test Coverage: Use the coverage reports to guide your testing efforts. Write additional tests to cover the uncovered parts of your code. Focus on critical or high-risk areas first.
  7. Track Progress: Continuously track your code coverage over time. Use it as a metric for quality improvement. Set goals to gradually increase coverage in key areas.
  8. Integrate into CI/CD: If you’re using Continuous Integration/Continuous Deployment (CI/CD), integrate code coverage measurement into your CI/CD pipeline. This ensures that coverage is checked automatically whenever code changes are pushed.
  9. Collaborate with the Team: Share coverage reports with your development team, and encourage collaboration to improve coverage collectively.

By following these steps and integrating code coverage measurement into your development process, you can gain valuable insights into your testing efforts and improve the overall quality of your codebase.

Code coverage measurement tools for Kotlin and Swift

Here are some popular tools for code coverage measurement in Kotlin and Swift:


  1. JaCoCo for Kotlin (Java Code Coverage): JaCoCo is a widely used code coverage tool for Java, but it can also be used with Kotlin projects. It provides detailed reports on code coverage, including line and branch coverage. It’s often integrated with build tools like Gradle and Maven.
  2. Kover: Gradle plugin that measures the coverage for tests running on the JVM and generates coverage reports.


  1. Xcode Code Coverage: Xcode, the official development environment for iOS/macOS applications, includes built-in code coverage tools. You can enable code coverage in your Xcode project’s scheme settings, and Xcode will generate code coverage reports after running tests.
    Xcode Code Coverage
  2. xcov: xcov is a command-line tool that helps you generate Xcode code coverage reports. It’s useful for integrating code coverage measurement into your CI/CD pipelines.
  3. Slather: Slather is another command-line tool for generating Xcode code coverage reports. It’s designed to work with popular CI/CD services and provides coverage metrics.

Additionally, consider the specific requirements of your project, including the build system and testing framework you’re using, as these factors can influence the choice of a code coverage tool and its integration into your development workflow.

Specifics of code coverage measurement

Measuring code coverage is a useful tool for evaluating test coverage, but it also has some drawbacks and limitations:

  • Coverage does not guarantee correctness: High code coverage does not mean that your program is completely correct. It only indicates that a certain percentage of the code has been tested. Effective testing also requires taking into account a variety of use cases and boundary cases that code coverage does not always detect.
  • Test Criticality: Code coverage can be a pretty good indicator for non-critical systems, but critical systems may require a higher level of reliability that is not always associated with high coverage.
  • Focus on quantity rather than quality of tests: Developers can be tempted to write tests just to increase the percentage of code coverage, without considering their actual effectiveness or quality. This approach can lead to the creation of meaningless tests that don’t detect real bugs.
  • Measuring only executed code: Coverage measurement tools may only focus on the code that was executed during testing. This means they don’t account for possible bugs in unused code or unaccounted execution paths.
  • Ignoring logic: Code coverage is not always able to detect logical errors, which can occur even when all code branches and instructions are covered. This limitation can be overcome by more sophisticated types of static and dynamic code analysis.

Despite these disadvantages, code coverage remains a useful tool when used correctly and combined with other methods of testing and code analysis. It is important to understand that it is not the only criterion of program quality.