Short Answer 
To troubleshoot JaCoCo coverage data issues, verify your JaCoCo plugin configuration in your build files and ensure tests are executed properly without any skipping flags. Additionally, check that the .exec execution data file is generated in the expected location and consult logs for potential errors.
Step 1: Verify JaCoCo Configuration
Check your build configuration files, such as Maven or Gradle, to ensure that the JaCoCo plugin is correctly set up. Look for any configuration errors that might prevent the JaCoCo agent from being attached properly. Pay attention to the following items:
- Correct version of JaCoCo specified in the plugin.
- Proper execution setup in the build lifecycle.
- Any additional configuration parameters that need to be set.
Step 2: Confirm Test Execution
Make sure that your tests are actually being executed, as the error often indicates that the JaCoCo agent did not collect any coverage data. Investigate the following aspects to ensure tests run correctly:
- Check if tests are included in your run command without the `-DskipTests` flag.
- Examine any conditions or configurations that could prevent tests from executing.
- Run tests in a clean environment to eliminate issues from previous runs.
Step 3: Validate Execution Data Generation
After ensuring that JaCoCo is configured correctly and tests are run, the next step is to validate that the .exec execution data file is being generated properly. It’s crucial to check the following:
- Ensure the .exec file is located in the expected directory.
- Review logs for any errors related to JaCoCo and execution data generation.
- Consult JaCoCo documentation or community forums for further troubleshooting if problems continue.