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JUnit 5 at Heisenbug 2017

JUnit 5 at Heisenbug 2017

Over the last decade a lot has happened in the world of Java and testing, but JUnit 4 hasn't kept up. Now JUnit 5 is here to help shape the future of testing on the JVM with a focus on Java 8 language features, extensibility, and a modern programming API for testing in Java. Moreover, JUnit isn't just a Java testing framework anymore. Third parties are already developing test engines for Scala, Groovy, Kotlin, etc. that run on the new JUnit Platform.

In this session, we will start off with an example-driven tour of the new Jupiter programming model and learn how to migrate our existing JUnit 4 based tests. Then, we will discuss the inspiration for JUnit 5, look more closely at its architecture, and discuss compatibility with JUnit 4. Next, we will explore the Jupiter extension model, learn about the extension points it provides, and see how custom extensions for conditional tests, method parameter resolution, lifecycle callbacks etc. are authored and registered. To round off the session, we will look at the roadmap of what's still to come and when you can expect the GA release.

Marc Philipp

June 04, 2017

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  1. Marc Philipp • Senior Software Engineer @ in Germany •

    JUnit Maintainer since 2012 • Twitter: @marcphilipp • Web: http://www.marcphilipp.de
  2. Meta Annotations Annotations can be combined to enable re-use:

 public @interface IntegrationTest {} Usage:
 void test() {}
 void test() {}
  3. @ParameterizedTest Sources • @ValueSource(ints = { 1, 2, 3 })

    • @EnumSource(TimeUnit.class) • @MethodSource(names = "myProviderMethod") • @CsvSource({ "foo, 1", "bar, 2", "'baz, qux', 3" }) • @CsvFileSource(resources = "/two-column.csv") • @ArgumentsSource(MyArgumentsProvider.class) • @YourCustomSource
  4. @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() {/* ... */} // ... } } }
  5. Dynamic Tests @TestFactory Stream<DynamicTest> dynamicTestsFromStream() { return IntStream.iterate(0, n ->

    n + 2).limit(100) .mapToObj(n -> dynamicTest("test" + n, () -> { assertTrue(n % 2 == 0); })); }
  6. 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
  7. 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
  8. Design Goals for JUnit 5 • Modern programming model for

    writing tests (Java 8!) • Powerful extension model with a focus on composability • API Segregation: Decouple test execution/reporting from test definition • Compatibility with older releases + migration path • Modularization + no external dependencies
  9. 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)
  10. 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
  11. 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
  12. 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
  13. Compatibility • Backward compatibility (junit-vintage-engine) enables gradual migration of tests

    to Jupiter API • Forward compatibility (JUnitPlatform Runner) allows test execution with “old” tools
  14. 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 • Opt-in support for registration via ServiceLoader
  15. Extension Points • Conditional Test Execution • ContainerExecutionCondition • TestExecutionCondition

    • General Purpose • TestInstancePostProcessor • ParameterResolver • TestTemplateInvocationContext- Provider • Test Lifecycle Callbacks • BeforeAllCallback • BeforeEachCallback • BeforeTestExecutionCallback • TestExecutionExceptionHandler • AfterTestExecutionCallback • AfterEachCallback • AfterAllCallback
  16. Roadmap • 5.0 M4 (April 2017): parameterized and repeated tests

    ✔ • 5.0 M5 (June 2017): dynamic containers and minor API changes • 5.0 M6 (July 2017): Java 9 compatibility, scenario tests, additional extension APIs for JUnit Jupiter • 5.0 RC1 (July 2017): Last fixes before GA • 5.0 GA (August 2017): First general availability release
  17. What’s in it for me? • Modern programming model •

    Powerful extension points • Gentle migration path • Good tool support • Flexible platform/plugin architecture
  18. Getting Started User Guide:
 http://junit.org/junit5/docs/current/user-guide/ Sample projects for Gradle and

 https://github.com/junit-team/junit5-samples Javadoc: