JUnit 5 

Marc Philipp • Senior Software Engineer @ in Germany • JUnit Maintainer since 2012 • Twitter: @marcphilipp • Web: http://www.marcphilipp.de 

Programming Model 

DEMO 

Meta Annotations Annotations can be combined to enable re-use:
 
 @Target(ElementType.METHOD)
 @Retention(RetentionPolicy.RUNTIME)
 @Tag("fast")
 @Test
 public @interface FastTest {} Usage:
 
 @FastTest
 void test() {}
 Equivalent:
 
 @Tag("fast")
 @Test
 void test() {} 

@Nested Tests @DisplayName("A stack") class TestingAStackDemo { @Test @DisplayName("is instantiated with new Stack()") void isInstantiatedWithNew() {/* ... */} @Nested @DisplayName("when new") class WhenNew { @BeforeEach void createNewStack() {/* ... */} @Test @DisplayName("is empty") void isEmpty() {/* ... */} // ... @Nested @DisplayName("after pushing an element") class AfterPushing { @BeforeEach void pushAnElement() {/* ... */} @Test @DisplayName("it is no longer empty") void isNotEmpty() {/* ... */} // ... } } } 

Dynamic Tests @TestFactory Stream dynamicTestsFromStream() { return IntStream.iterate(0, n -> n + 2).limit(100) .mapToObj(n -> dynamicTest("test" + n, () -> { assertTrue(n % 2 == 0); })); } 

Why do we need a new JUnit? 

Runner • Very powerful: Almost every aspect of test execution can be changed • But: You can only have one Runner per test class! • You can’t combine Runners, e.g.
 SpringJUnit4ClassRunner + Parameterized 

Rules • Extension mechanism introduced in JUnit 4.7 • Wraps execution of a test (@Rule) or a test class (@ClassRule) • Designed to be combined — great for simple use cases • But: a single rule cannot be used for method-level and class-level callbacks, no support for instance-level callbacks 

http://blog.takipi.com/the-top-100-java-libraries-in-2016-after-analyzing-47251-dependencies/ 

Existing Architecture Everyone uses the junit.jar. 

Renaming a private field should not break anything, right? 4.11 4.12-beta-1 

–Johannes Link, https://jaxenter.com/crowdfunding-for-junit-lambda-is- underway-119546.html „The success of JUnit as a platform prevents the development of JUnit as a tool.“ 

Modularization 

Separation of Concerns 1. An API to write tests (Jupiter API) 2. Extensible mechanisms to discover and execute tests (Test Engine SPI) 3. An API for test execution by tools (Launcher API) 

P L AT F O R M J U P I T E R V I N TA G E P A R T Y T H I R D 

P L AT F O R M J U P I T E R V I N TA G E P A R T Y T H I R D 

JUnitPlatform Runner for a single class import org.junit.jupiter.api.Test; @RunWith(JUnitPlatform.class) public class JupiterTest { @Test void someTest() { // test something } } 

JUnitPlatform Runner in suite mode @RunWith(JUnitPlatform.class) @SelectPackages("com.acme") @IncludeEngines({"junit-jupiter", "junit-vintage"}) public class JUnit4SuiteDemo { // this class can be run using JUnit 4 } 

Test Execution • IDEs: • IntelliJ supports JUnit 5 ≥ M2 since 2016.2 • Eclipse support is available on a branch (see Instructions).
 Official release slated for Oxygen.1. • Interim solution for other IDEs: JUnitPlatform Runner • Gradle/Maven: Plugin/Provider available • see https://github.com/junit-team/junit5-samples • Manually: ConsoleLauncher 

Compatibility • Backward compatibility (junit-vintage-engine) enables gradual migration of tests to Jupiter API • Forward compatibility (JUnitPlatform Runner) allows test execution with “old” tools 

Extensions 

Registration via @ExtendWith • Annotate your test classes or methods to register extensions • Supports an arbitrary number of extensions at the same time • May be used as a meta-annotation 

DEMO 

Extension Points • Conditional Test Execution • ContainerExecutionCondition • TestExecutionCondition • General Purpose • TestInstancePostProcessor • TestExecutionExceptionHandler • ParameterResolver • Test Lifecycle Callbacks • BeforeAllCallback • BeforeEachCallback • BeforeTestExecutionCallback • AfterTestExecutionCallback • AfterEachCallback • AfterAllCallback 

Roadmap 

M4: @ParameterizedTest class ParameterizedTests { @ParameterizedTest @CsvSource({ "foo, 1", "bar, 2" }) void testWithParametersFromAnnotation(String parameter, int i) { // test something } @ParameterizedTest @MethodSource(names = "providerMethod") void testWithParametersFromMethods(String parameter) { } static Iterable providerMethod() { return asList("foo", "bar"); } @ParameterizedTest @CsvFileSource(resources = { "foo.csv", "/bar.csv" }) void testWithParametersFromFile(String parameter) { } } 

M4: @RepeatedTest @RepeatedTest(10) void repeatedTest() { // ... } 

Roadmap to GA • 5.0.0-M4 (April 2017): Parameterized/RepeatedTests • 5.0.0-M5 (?) (May 2017): Java 9 compatibility • 5.0.0-RC1 (June 2017): Last fixes before GA • 5.0.0 (July 2017): GA 

Getting Started User Guide:
 http://junit.org/junit5/docs/current/user-guide/ Sample projects for Gradle and Maven:
 https://github.com/junit-team/junit5-samples Javadoc:
 http://junit.org/junit5/docs/current/api/ 

Wanted: Feedback! Website:
 http://junit.org/junit5/ Code & Issues:
 https://github.com/junit-team/junit5/ Twitter:
 https://twitter.com/junitteam