Selecting tests by tags and classes in JUnit - Test Execution Trace

Test Overview

This test suite demonstrates how to select and run specific tests in JUnit 5 by using tags and test classes. It verifies that only tests with the specified tag or in the specified class are executed.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import org.junit.platform.launcher.Launcher;
import org.junit.platform.launcher.LauncherDiscoveryRequest;
import org.junit.platform.launcher.LauncherDiscoveryRequestBuilder;
import org.junit.platform.launcher.core.LauncherFactory;
import org.junit.platform.launcher.listeners.SummaryGeneratingListener;
import org.junit.platform.engine.discovery.DiscoverySelectors;
import org.junit.platform.engine.discovery.TagFilter;

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

public class TagAndClassSelectionTest {

    @Tag("fast")
    @Test
    void fastTest() {
        assertEquals(2, 1 + 1);
    }

    @Tag("slow")
    @Test
    void slowTest() {
        assertEquals(4, 2 * 2);
    }

    @Test
    void untaggedTest() {
        assertEquals(3, 1 + 2);
    }

    public static void main(String[] args) {
        SummaryGeneratingListener listener = new SummaryGeneratingListener();

        // Build request to select tests tagged with 'fast'
        LauncherDiscoveryRequest requestByTag = LauncherDiscoveryRequestBuilder.request()
                .selectors(DiscoverySelectors.selectClass(TagAndClassSelectionTest.class))
                .filters(TagFilter.includeTags("fast"))
                .build();

        Launcher launcher = LauncherFactory.create();
        launcher.registerTestExecutionListeners(listener);
        launcher.execute(requestByTag);

        long testsFoundByTag = listener.getSummary().getTestsFoundCount();
        long testsSucceededByTag = listener.getSummary().getTestsSucceededCount();

        System.out.println("Tests found with tag 'fast': " + testsFoundByTag);
        System.out.println("Tests succeeded with tag 'fast': " + testsSucceededByTag);

        // Reset listener for next run
        listener = new SummaryGeneratingListener();

        // Build request to select tests by class only (all tests in this class)
        LauncherDiscoveryRequest requestByClass = LauncherDiscoveryRequestBuilder.request()
                .selectors(DiscoverySelectors.selectClass(TagAndClassSelectionTest.class))
                .build();

        launcher.registerTestExecutionListeners(listener);
        launcher.execute(requestByClass);

        long testsFoundByClass = listener.getSummary().getTestsFoundCount();
        long testsSucceededByClass = listener.getSummary().getTestsSucceededCount();

        System.out.println("Tests found by class: " + testsFoundByClass);
        System.out.println("Tests succeeded by class: " + testsSucceededByClass);

        // Assertions to verify behavior
        assertEquals(1, testsFoundByTag, "Should find exactly 1 test with tag 'fast'");
        assertEquals(1, testsSucceededByTag, "The tagged test should pass");
        assertEquals(3, testsFoundByClass, "Should find all 3 tests in the class");
        assertEquals(3, testsSucceededByClass, "All tests in the class should pass");
    }
}

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	Test starts - JUnit launcher is created	No tests executed yet	-	PASS
2	LauncherDiscoveryRequest built to select tests tagged with 'fast' in TagAndClassSelectionTest class	Request ready to find tests with tag 'fast'	-	PASS
3	Launcher executes tests matching the 'fast' tag	Only the test method 'fastTest' is found and executed	Verify test 'fastTest' passes	PASS
4	Summary shows 1 test found and passed for tag 'fast'	Test summary reports 1 test found and succeeded	Assert testsFoundByTag == 1 and testsSucceededByTag == 1	PASS
5	LauncherDiscoveryRequest built to select all tests in TagAndClassSelectionTest class	Request ready to find all tests in the class	-	PASS
6	Launcher executes all tests in the class	All three test methods (fastTest, slowTest, untaggedTest) are found and executed	Verify all tests pass	PASS
7	Summary shows 3 tests found and passed for class selection	Test summary reports 3 tests found and succeeded	Assert testsFoundByClass == 3 and testsSucceededByClass == 3	PASS
8	Test ends successfully with all assertions passing	All tests executed as expected	-	PASS

Failure Scenario

Failing Condition: No tests found with the specified tag due to typo or missing tag annotation

Execution Trace Quiz - 3 Questions

Which test method is executed when selecting tests by tag 'fast'?

A fastTest

B slowTest

C untaggedTest

D All tests in the class

Key Result

Using tags and class selectors in JUnit allows you to run focused subsets of tests, which helps speed up testing and organize tests by categories.