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.

Transcript

1. JUnit 5
   

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

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3. Programming Model
   

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4. DEMO
   https://github.com/marcphilipp/junit5-demo/tree/20170604-heisenbug
   

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5. Meta Annotations
   Annotations can be combined to enable re-use:

   

   @Target(ElementType.METHOD)

   @Retention(RetentionPolicy.RUNTIME)

   @Tag("integration")

   @Test

   public @interface IntegrationTest {}
   Usage:

   

   @IntegrationTest

   void test() {}

   Equivalent:

   

   @Tag("integration")

   @Test

   void test() {}
   

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6. @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
   

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7. @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() {/* ... */}
   // ...
   }
   }
   }
   

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

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9. @RepeatedTest
   @RepeatedTest(10)
   void repeatedTest() {
   // ...
   }
   

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10. Why do we need a new
    JUnit?
    

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11. 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
    

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12. 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
    

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

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14. Existing Architecture
    Everyone uses the junit.jar.
    

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

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16. –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.“
    

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17. 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
    

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18. Modularization
    

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19. 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)
    

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20. 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
    

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21. 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
    

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

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23. 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
    }
    

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24. 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
    

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

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26. Extensions
    

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27. 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
    

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28. DEMO
    https://github.com/marcphilipp/junit5-demo/tree/20170604-heisenbug
    

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

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30. 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
    

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31. Summary
    

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32. What’s in it for me?
    • Modern programming model
    • Powerful extension points
    • Gentle migration path
    • Good tool support
    • Flexible platform/plugin architecture
    

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33. 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/
    

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34. Wanted: Feedback!
    Website:

    http://junit.org/junit5/
    Code & Issues:

    https://github.com/junit-team/junit5/
    Twitter:

    https://twitter.com/junitteam
    

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