JaCoCo Coverage Data Write Behavior | Generated by AI
In integration tests (or any JVM process) using the JaCoCo agent, the coverage data is not automatically written to the .exec file when the JVM exits. Here’s how it works:
When Does JaCoCo Write Coverage Data?
- During JVM Shutdown: The JaCoCo agent flushes and writes the collected coverage data to the
.execfile when the JVM shuts down gracefully (e.g., when the main method ends or the test suite completes). - If the JVM Crashes: If the JVM terminates abruptly (e.g., due to a crash or
System.exit()), the agent may not have a chance to write the data, and some coverage information could be lost.
How to Ensure Data is Written
- Graceful Shutdown: Ensure your integration tests or application ends normally (e.g., no forced exits).
- Explicit Dump (Optional): You can manually trigger a dump of coverage data during runtime using the JaCoCo runtime API (e.g.,
org.jacoco.agent.rt.RT.getAgentRuntime().dump(true, outputFile)). This is useful for long-running processes or if you want to capture intermediate data.
Example Scenario
- If your integration test suite runs and completes normally, the JaCoCo agent will write the coverage data to
jacoco.exec(or your specified file) at the end of the JVM process. - If the JVM is killed (e.g.,
kill -9), the data may not be written.
Best Practice
- Use
append=true: If you run multiple test suites, setappend=truein the JaCoCo agent arguments to accumulate coverage data across runs. - Check for Partial Data: If the JVM crashes, the
.execfile might be incomplete or missing data for the last run.