Catching up with JUnit 5

Almost 8 years have passed since the initial release of JUnit 5. But a lot has happened since then! In 12 additional feature releases the JUnit team has continually enhanced the expressiveness of the testing framework and the flexibility of the platform. This workshop is for everyone who is interested in a introduction to JUnit or who wants to catch up with the latest features and enhancements by doing hands-on exercises.

We will start with the basics, explain the lifecycle of tests and which possibilities exist for influencing it. Assertions, display names, tags, order and timeouts will be additional topics. We will then focus on parameterized tests, including custom argument sources. Last but not least, we are going to go into detail on JUnit Jupiter's extension model, introduce its core extensions, and write custom extensions together.

Transcript

1. Catching up with JUnit 5 JCON Europe – May 12, 2025
2. Marc Philipp
3. Christian Stein
4. Thank you to our sponsors!
5. JUnit experience?
6. Architecture JU N I T 5 P L AT F O R M Another Test PA R T Y T H I R D JU P I T E R VI N TAG E
7. JUnit Jupiter P L AT F O R M JU P I T E R
8. JUnit Jupiter API • → • →
9. Writing Tests with Jupiter
10. Basics import org.junit.jupiter.api.Test; import static org.junit.jupiter.api.Assertions.assertEquals; class Tests { @Test void onePlusOneIsTwo() { assertEquals(2, 1 + 1); } }
11. Exercise 1: Basics (15m) ./gradlew build ./mvnw clean verify @Disabled Exercise01_ListTests @BeforeEach
12. Display Names • @DisplayName • @DisplayNameGeneration @DisplayName • junit.jupiter.displayname.generator.default
13. Display Name Generators @DisplayNameGeneration(ReplaceUnderscores.class) class A_year_is_not_supported { @Test void if_it_is_zero() {/*���*/} @ParameterizedTest @ValueSource(ints = { -1, -4 }) void if_it_is_negative(int year) {/*���*/} }
14. Exercise 2: Display Names (10m) Exercise01_ListTests @DisplayName("A list") @DisplayNameGeneration(ReplaceUnderscores.class) @DisplayNameGeneration src/test/resources/junit- platform.properties junit.jupiter.displayname.generator.default = \ org.junit.jupiter.api.DisplayNameGenerator$ReplaceUnderscores
15. Tags • @Tag • @Tag
16. Exercise 3: Tags (10m) @Tag("exercise-3") tasks.test { useJUnitPlatform { includeTags("exercise-3") } } <plugin> <artifactId>maven-surefire-plugin��artifactId> <version>3.5.3��version> <configuration> <groups>exercise-3��groups> ��configuration> ��plugin>
17. Nested Tests • @Nested •
18. Exercise 4: Nested Tests (10m) @Nested TwoElements OneElement Exercise04_ListTests TwoElements OneElement
19. Timeouts • assertTimeout{Preemptively} • @Timeout • junit.jupiter.execution.timeout.{���}.default
20. Exercise 5: Timeouts (10m) @Disabled Exercise05_TimeoutTests sleep() sleep()
21. Exercise 5: Timeouts (answers) 1/2 • assertTimeout • assertTimeoutPreemptively @Timeout
22. Exercise 5: Timeouts (answers) 2/2 • assertTimeout{Preemptively} AssertionFailedError @Timeout TimeoutException • @Timeout @Transactional ▪ @Timeout(threadMode = SEPARATE_THREAD)
23. Parameterized Tests • @ParameterizedTest @Test @���Source • @ValueSource @EnumSource @CsvSource @CsvFileSource @MethodSource @FieldSource @NullSource @EmptySource @ArgumentsSource(MyProvider.class)
24. Exercise 6: Parameterized Tests (10m) sqrt Exercise06_MathTests @ParameterizedTest Math.floor @MethodSource @CsvSource
25. Jupiter Extensions
26. Extension Marker Interface • Extension • • package org.junit.jupiter.api.extension; /** * Marker interface for all extensions. * ��� �� public interface Extension {}
27. Extension Point (Conditional Execution) ExecutionCondition public interface ExecutionCondition extends Extension { /** * Evaluate this condition for the supplied {@code ExtensionContext}. * ��� * @param context the current extension context; never {@code null} * @return the result of evaluating this condition; never {@code null} �� ConditionEvaluationResult evaluateExecutionCondition( ExtensionContext context ); }
28. Extension Context • Extension • • public interface ExecutionCondition extends Extension { /** * Evaluate this condition for the supplied {@code ExtensionContext}. * ��� * @param context the current extension context; never {@code null} * @return the result of evaluating this condition; never {@code null} �� ConditionEvaluationResult evaluateExecutionCondition( ExtensionContext context ); }
29. Extension Context Hierarchy root : ExtensionContext displayName = "JUnit Jupiter" parent class1 : ExtensionContext displayName = "TestClass1" parent test1 : ExtensionContext displayName = "test1()" parent test2 : ExtensionContext displayName = "test2()" parent class2 : ExtensionContext displayName = "TestClass2" parent test3 : ExtensionContext displayName = "test3()"
30. Support Classes org.junit.platform.commons.support • AnnotationSupport • ReflectionSupport
31. Exercise 7: Execution Conditions (10m) ExecutionCondition @NotToday ExtensionContext.getElement() AnnotationSupport.isAnnotated() @ExtendWith(NotTodayExtension.class) class Exercise08_Tests { @NotToday @Test void test() { �� ��� �� } } class NotTodayExtension implements ExecutionCondition { �� ��� �� }
32. Composed Annotations @Retention(RUNTIME) @Target(METHOD) @Test @Tag("example") public @interface ExampleTest {}
33. Exercise 8: Composed Annotations (5m) @ExtendWith Exercise08_Tests NotToday @ExtendWith(NotTodayExtension.class) Exercise09_Tests
34. Extension Points (Lifecycle) • BeforeAllCallback ▪ BeforeClassTemplateInvocationCallback ◦ BeforeEachCallback ◦ BeforeTestExecutionCallback ◦ AfterTestExecutionCallback ◦ AfterEachCallback ▪ AfterClassTemplateInvocationCallback • AfterAllCallback
35. Extension Points (Parameter Resolver) • ParameterResolver • TypeBasedParameterResolver
36. Exercise 9 (10m): Reusable Setup ExecutorServiceExtension BeforeAllCallback AfterAllCallback TypeBasedParameterResolver<ExecutorService> Exercise09_TestsA B ExecutorServiceExtension ExecutorService @ExtendWith(ExecutorServiceExtension.class) class Exercise09_TestsA { @Test void test(ExecutorService executorService) { �� ��� �� } }
37. More Extension Points • •
38. More Core Extensions • @RepeatedTest @Test • @TempDir • @AutoClose • @ParameterizedClass @ParameterizedTest
39. Built-in Conditions (1/2) • @Enabled DisabledOnOs({LINUX, MAC, …}) ▪ architectures = "aarch64" • @Enabled DisabledOnJre({JAVA_11, …}) • @Enabled DisabledForJreRange(min = JAVA_9, max = JAVA_10)
40. Built-in Conditions (2/2) • @Enabled DisabledIfSystemProperty(named = "someKey", matches = "someValue") • @Enabled DisabledIfEnvironmentVariable(named = "SOME_KEY", matches = "SOME_VALUE") • @Enabled DisabledIf("customCondition") • @Enabled DisabledInNativeImage
41. Built-in Parameter Resolvers • TestInfo • RepetitionInfo @RepeatedTest • ParameterInfo @ParameterizedClass @ParameterizedTest • TestReporter
42. Third-Party Extensions
43. Wrapping Up
44. Today’s Blind Spots • • • • • • • •
45. In-House Workshop Offering • • • • •
46. Links • • • •
47. Exercise Solutions solutions
48. Thank you!