JaCoCo setup and configuration in JUnit - Test Execution Trace

Test Overview

This test checks that JaCoCo code coverage is correctly set up and configured in a JUnit test environment. It verifies that the coverage agent runs and reports coverage data after executing a simple test case.

Test Code - JUnit 5

JUnit

import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.api.Test;

public class SampleServiceTest {

    @Test
    public void testIsPositive() {
        SampleService service = new SampleService();
        boolean result = service.isPositive(5);
        assertTrue(result, "Number should be positive");
    }
}

class SampleService {
    public boolean isPositive(int number) {
        return number > 0;
    }
}

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test execution starts with JUnit runner	JUnit test runner initialized, JaCoCo Java agent attached to JVM	-	PASS
2	JUnit runner invokes SampleServiceTest.testIsPositive()	SampleServiceTest instance created, method isPositive called with argument 5	-	PASS
3	SampleService.isPositive(5) returns true	Method returns boolean true as 5 > 0	-	PASS
4	JUnit assertion assertTrue(result) verifies the returned value is true	Assertion passes because result is true	assertTrue(result) == true	PASS
5	JUnit test completes successfully	Test method finished without exceptions	-	PASS
6	JaCoCo agent collects coverage data during test execution	Coverage data recorded for SampleService.isPositive method	-	PASS
7	Build tool generates JaCoCo coverage report after tests	Report shows coverage percentage including SampleService.isPositive method	Coverage report includes SampleService.isPositive with coverage > 0%	PASS

Failure Scenario

Failing Condition: JaCoCo agent is not attached or misconfigured, so coverage data is not collected

Execution Trace Quiz - 3 Questions

What confirms that the test method executed successfully?

A SampleService.isPositive method returns false

B JaCoCo coverage report is generated

C JUnit assertion assertTrue(result) passes

D JUnit runner fails to start

Key Result

Always verify that the JaCoCo agent is properly attached to the JVM and that the build tool is configured to generate coverage reports after tests run. This ensures accurate coverage measurement.