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from Lambda to Alpha and Beyond …
Sam Brannen
@sam_brannen
JUnit

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Sam Brannen
• Spring and Java Consultant @
• Java Developer for over 17 years
• Spring Framework Core Committer since 2007
• Swiss Spring User Group Lead
• Trainer & Conference Speaker
• JUnit 5 Core Committer since October 2015

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Swiftmind
Experts in Spring and Enterprise Java
Areas of expertise
• Spring *
• Java EE
• Software Architecture
• Software Development
Where you find us
• Zurich, Switzerland
• @swiftmind
• http://www.swiftmind.com

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A Show of Hands…

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Agenda
• Impetus for Change
• JUnit Lambda
• Roadmap
• JUnit 5
• Feedback
• Q&A

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Impetus for Change

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Why a New Version of JUnit?
• JUnit 4.0 was released a decade ago
– a lot has changed since then…
– testing needs have matured
– expectations have grown
• Modularity  big ball of mud
• Test discovery and execution  tightly coupled
• Extensibility  lot of room for improvement
• Let’s not forget Java 8

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Modularity in JUnit 4
• Sure there are packages
– but… there’s only THE junit.jar

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JUnit 4 Runner API
• Very powerful
• In fact, it can do anything
• But… you can’t combine Runners
• Parameterized + SpringJUnit4ClassRunner  no way

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JUnit 4… Rules… are meant to be broken
• JUnit 4.7: MethodRule (@Rule)
• JUnit 4.9: TestRule (@Rule / @ClassRule)
• Great for simple use cases
• Can even be combined
• But… a single rule can’t be used for method-level and
class-level callbacks
• Plus… zero support for instance-level callbacks
• Case in point: SpringClassRule / SpringMethodRule

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JUnit Lambda

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Crowdfunding Campaign
• Initiated by Johannes Link and
Marc Philipp
• Later joined by Matthias Merdes,
Stefan Bechtold, & Sam Brannen
• Ran from July to October 2015
• Raised 53,937 Euros from 474
individuals and companies
• 4 companies donated 6 weeks of
developer time

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Thanks!

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The Kick-off Team

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Roadmap
• Prototype  December 2nd, 2015
• 5.0.0-ALPHA  February 1st, 2016
• 5.0.0-M1  in progress
– tentative release end of June 2016
• M2, M3, …  Summer 2016
• RC1, RC2, ...  Fall 2016
• GA  late 2016

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JUnit 5

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JUnit 5… in a Nutshell
• Modular
• Extensible
• Modern
• Forward and backward compatible
– JUnit 5 supports JUnit 3.8 and JUnit 4
– Can be run with JUnit 4
• @RunWith(JUnit5.class)

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Architecture
• Test code depends only on
the JUnit 5 API.
• IDEs and build tools
depend on the Launcher
and Engine APIs and can
execute tests independent
of the testing framework
in use.

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Modules
• junit5-api
• junit-launcher
• junit-engine-api
• junit5-engine
• junit4-engine
• junit4-runner
• junit-commons
• junit-console
• junit-gradle
• surefire-junit5

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Launcher API
• Used by IDEs and build tools to launch the framework
• Central API for discovering and executing tests via one or
more engines
• TestDiscoveryRequest
– selectors and filters
• Feedback provided via the TestExecutionListener API

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TestEngine API
• Test engine discovers and executes tests
– for a particular programming model
• Automatic discovery via Java’s ServiceLoader mechanism
• JUnit5TestEngine
• JUnit4TestEngine
• Implement your own…

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JUnit 5 Extension Model
org.junit.gen5.api.extensions  @ExtendWith(...)
• BeforeAllCallback
• BeforeEachCallback
• BeforeTestExecutionCallback
• AfterTestExecutionCallback
• AfterEachCallback
• AfterAllCallback
• ContainerExecutionCondition
• TestExecutionCondition
• TestInstancePostProcessor
• ParameterResolver
• TestExecutionExceptionHandler

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JUnit 5 Programming Model
org.junit.gen5.api
• Annotations and meta-annotations
• Assertions and Assumptions
• Custom display names
• Visibility
• Tagging
• Conditional test execution
• Dependency injection for constructors and methods
• Lambda expressions and method references
• Interface default methods
• Nested test classes

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Annotations
• @Test
• @BeforeAll / @AfterAll
• @BeforeEach / @AfterEach
• @DisplayName
• @Tag / @Tags
• @Disabled
• @Nested

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Assertions
org.junit.gen5.api.Assertions
• Limited set of core assertions
– assertEquals(), assertNotNull(), etc.
– plus assertThrows() and expectThrows()
– and assertAll()
• Supplier<String>  for lazy failure message evaluation
– message is now the last parameter
• For more power, use AssertJ, Hamcrest, etc.

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Assumptions
org.junit.gen5.api.Assumptions
• Limited set of core assumptions
– For aborting tests mid-flight
• assumeTrue() / assumeFalse()
– BooleanSupplier, Supplier<String>
• assumingThat( ? , () -> {} );

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DEMO

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Test Names
• Names default to test class or test method names
– characters limited based on Java syntax
• Custom display names  @DisplayName
– Can contain spaces, special chars, and even emoji 😱

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Dependency Injection
• Extension Model meets Programming Model
• ParameterResolver extension
– resolves parameters for constructors or methods
• TestInfo: inject into constructor, @Test, @BeforeEach, etc.
– access display name, tags, class, method
• TestInfoParameterResolver
– eating our own dog food ;-)
• See also:
– TestReporter
– MockitoExtension
– SpringExtension

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DEMO

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Tagging
• Declare @Tag or @Tags on an interface, class, or method
@Tag("fast")
@Test
void myFastTest() {
}

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Custom Tags
• Declare @Tag or @Tags as a meta-annotation
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Tag("fast")
@Test
public @interface FastTest {
}
@FastTest
void myFastTest() {
}

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Conditional Test Execution
• Extension Model meets Programming Model
• ContainerExecutionCondition
• TestExecutionCondition
• @Disabled
• DisabledCondition
– eating our own dog food ;-)
• Deactivate via Launcher/System property
– junit.conditions.deactivate = org.junit.*

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DEMO

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Interface Default Methods
• Introduces the concept of a test interface
– Enables multiple inheritance in tests
– Kinda like testing traits
• @BeforeEach / @AfterEach
• @Test
• @Tag
• @ExtendWith
• See StringTests example in user guide

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Nested Test Classes
• Enables logical, hierarchical grouping of test classes
– with shared initialization and state from outer classes
• Declare @Nested on non-static nested classes
– i.e., inner classes
• You can even combine nested classes and test interfaces
• See TestingAStack example in user guide

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Spring Support for JUnit 5
• SpringExtension
– @ExtendWith(SpringExtension.class)
– https://github.com/sbrannen/spring-test-junit5
• Works with Spring Framework 4.3
• Already supports:
– Core Spring TestContext Framework features
– Constructor and method injection via @Autowired,
@Qualifier, @Value
• Fully integrated in Spring Framework 5.0

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DEMO

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In Closing…

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What’s Missing?
• Official IDE and build integration
• Dynamic tests (M1)
– registered as lambdas, streams, collections, etc.
• Parameterized tests (M2)
• Scenario tests (M3)
• Parallel execution (?)
• …

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Resources and Feedback Channels
• Project Homepage
– http://junit.org/junit5
• User Guide
– http://junit.org/junit5/docs/current/user-guide
• Javadoc
– https://junit.ci.cloudbees.com/job/JUnit5/javadoc
• GitHub
– https://github.com/junit-team/junit5
• Sample Projects
– https://github.com/junit-team/junit5-samples
• Twitter
– https://twitter.com/JUnitTeam
• Stack Overflow
– http://stackoverflow.com/tags/junit5

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Q & A
Sam Brannen
@sam_brannen
www.slideshare.net/sbrannen
www.swiftmind.com