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JUnit 5 - The New Testing Framework for Java and Platform for the JVM

JUnit 5 - The New Testing Framework for Java and Platform for the JVM

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 overview of the inspiration for and architecture of JUnit 5, from launchers to test engines. Then, we will take an example-driven tour of the new Jupiter programming model. 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 discuss migration strategies and compatibility with JUnit 4 and look at the roadmap of what's still to come.

Marc Philipp

March 23, 2017
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  1. Marc Philipp
    • Senior Software Engineer @ in Germany
    • JUnit Maintainer since 2012
    • Twitter: @marcphilipp
    • Web: http://www.marcphilipp.de

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  2. Programming Model

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  3. 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() {}

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  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() {/* ... */}
    // ...
    }
    }
    }

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  5. 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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  6. Why do we need a new
    JUnit?

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  7. 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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  8. 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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  9. http://blog.takipi.com/the-top-100-java-libraries-in-2016-after-analyzing-47251-dependencies/

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  10. Existing Architecture
    Everyone uses the junit.jar.

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

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  12. –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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  13. Modularization

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  14. 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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  15. 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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  16. 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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  17. 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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  18. 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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  19. 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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  20. 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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  21. 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

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

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  23. 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) {
    }
    }

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

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  25. 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

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  26. 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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  27. Wanted: Feedback!
    Website:

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

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

    https://twitter.com/junitteam

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