Testing with Spring, AOT, GraalVM, and JUnit 5 Sam Brannen @sam_brannen

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Sam Brannen ● Staff Software Engineer ● Java Developer for over 20 years ● Spring Framework Core Committer since 2007 ● JUnit 5 Core Committer since October 2015

Agenda ● JUnit 5.9, 5.10, 5.11 ● Spring 6.0 and 6.1 ● Spring AOT and GraalVM ● Demo

JUnit 5.9 https://junit.org/junit5/docs/5.9.3/release-notes/

JUnit Platform 1.9.x ● XML reports in new Open Test Reporting format ● https://github.com/ota4j-team/open-test-reporting ● New IterationSelector ● for selecting a subset of a test’s or container’s iterations ● Various improvements to ConsoleLauncher ● --single-color and --color-palette ● --list-engines ● JUnit Platform Suite Engine included in stand-alone JAR

JUnit Jupiter 5.9.x (1/2) ● Configurable cleanup mode for @TempDir ● ALWAYS, ON_SUCCESS, NEVER ● New TestInstancePreConstructCallback extension API ● counterpart to existing TestInstancePreDestroyCallback ● Reusable parameter resolution for method invocations ● via ExecutableInvoker API ● accessed via ExtensionContext ● used for @MethodSource factory methods ● @MethodSource factory methods can accept arguments ● resolved by ParameterResolver extensions ● new syntax to disambiguate local factory methods

JUnit Jupiter 5.9.x (2/2) ● Configurable thread mode for @Timeout ● INFERRED, SAME_THREAD, SEPARATE_THREAD ● @EnabledOnOs and @DisabledOnOs ● support for OS architectures ● support for FreeBSD and OpenBSD ● @EnabledInNativeImage and @DisabledInNativeImage ● enable/disable tests in GraalVM native image ● AssertionFailureBuilder ● reuse Jupiter’s logic for creating failure messages

JUnit 5.10 https://junit.org/junit5/docs/5.10.0-M1/release-notes/

JUnit Platform 1.10 M1 ● Promotion of various experimental APIs to stable ● Stacktrace pruning to hide internal JUnit calls ● ConsoleLauncher ● new testfeed details mode ● new discover subcommand for test discovery without execution ● Dry-run mode for test execution ● New LauncherInterceptor SPI ● New NamespacedHierarchicalStore for use in third-party test engines

Custom ClassLoader Arrangements ● New ReflectionSupport.tryToLoadClass(…) method that accepts an explicit ClassLoader ● ReflectionSupport.findMethod(Class>, String, String) ● now uses ClassLoader of the supplied class to load parameter types ● used by DiscoverySelectors.selectMethod(Class>, String, String) ● DiscoverySelectors methods for ClassSelector, NestedClassSelector, MethodSelector, and NestedMethodSelector that accept an explicit ClassLoader

JUnit Jupiter 5.10 M1 ● Promotion of various experimental APIs to stable ● Failure threshold for @RepeatedTest ● New TempDirFactory SPI for customizing @TempDir ● Custom ClassLoader support for @EnabledIf, @DisabledIf, @MethodSource, and @ParameterizedTest argument conversion ● Improved configurability of parallel execution ● AnnotationBasedArgumentsProvider/AnnotationBasedArgumentConverter ● base classes for implementing ArgumentsProvider and ArgumentConverter

JUnit 5.11 https://github.com/junit-team/junit5/milestone/68

Current Roadmap ● @BeforeSuite and @AfterSuite ● in JUnit Platform @Suite engine ● Extension API for customizing the ClassLoader in Jupiter ● @FieldSource for parameterized tests ● @ContainerTemplate ● analagous to @TestTemplate ● ContainerTemplateInvocationContextProvider extension API ● @ParameterizedContainer ● effectively parameterized test classes

@FieldSource @ParameterizedTest @FieldSource("example.Utils#fruits") void test(String fruit) { /* perform assertions */ } public class Utils { public static final String[] fruits = {"apple", "banana"}; }

@ParameterizedContainer – Field Injection @ParameterizedContainer @CsvSource({"apple, 1", "banana, 2"}) class FieldInjectionTestCase { @Parameter(0) private String fruit; @Parameter(1) private int score; @Test void test() { /* perform assertions */ } }

@ParameterizedContainer – Constructor Injection @ParameterizedContainer @CsvSource({"apple, 1", "banana, 2"}) class ConstructorInjectionTestCase { private final String fruit; private final int score; ConstructorInjectionTestCase(String fruit, int score) { this.fruit = fruit; this.score = score; } @Test void test() { /* perform assertions */ } }

@ParameterizedContainer – Java Record @ParameterizedContainer @CsvSource({"apple, 1", "banana, 2"}) record RecordTestCase(String fruit, int score) { @Test void test() { /* perform assertions */ } }

Spring 6.0 - 6.1

Spring 6.0.x ● Module path scanning for "classpath*:" resource prefix ● useful for patched test modules with Maven ● Servlet API 6.0 baseline in Servlet mocks and MockMvc ● with Servlet 5.0 compatibility at runtime ● Assertions against Cookie attributes in CookieResultMatchers for MockMvc ● Default TestExecutionListeners enabled in JUnit 4 and TestNG base test classes ● Revised logging in the TestContext framework (TCF) ● ApplicationContextFailureProcessor SPI for processing ApplicationContext failures in the TCF ● used by Spring Boot ● Ahead of Time and GraalVM native image support

Spring 6.1 ● Support for recording async events with @RecordApplicationEvents ● record events from threads other than main test thread ● assert events from separate thread – for example with Awaitility ● limitations in JUnit Jupiter ● Support for null in MockHttpServletResponse.setCharacterEncoding() ● New MockHttpServletRequestBuilder.setRemoteAddress() method ● Avoid repeated attempts to load failing ApplicationContext in the TestContext framework ● Potential integration with @ParameterizedContainer in JUnit Jupiter 5.11

Spring AOT and GraalVM

What are AOT and GraalVM? ● AOT ● ahead-of-time optimizations ● part of the build process ● utilized at runtime ● GraalVM – https://www.graalvm.org/ ● polyglot programming on the JVM ● native image ● compiling JVM applications to OS-specific binaries ● closed world assumptions ● no classpath ● requires runtime hints

What is Spring AOT? ● https://docs.spring.io/spring-framework/reference/core/aot.html ● AOT optimizations meant to inspect an ApplicationContext at build time and apply decisions and discovery logic that usually happens at runtime. ● Core infrastructure in Spring Framework ● Implemented across the portfolio ● Build tools in Spring Boot ● Spring AOT optimizations are used in GraalVM native image

AOT Support for Spring Integration Tests ● https://docs.spring.io/spring-framework/reference/testing/testcontext- framework/aot.html ● Build-time detection of Spring integration tests ● JUnit Jupiter, JUnit 4, and implicit support for TestNG etc. ● Build-time AOT processing ○ each unique test ApplicationContext will be refreshed for AOT processing ● Runtime AOT support ○ Spring integration tests use AOT-optimized ApplicationContexts

GraalVM Native Build Tools ● https://graalvm.github.io/native-build-tools/ ● Collaboration between Oracle Labs, Spring, and Micronaut ● Build native image ● Run tests in native image using the JUnit Platform ● Plugins for Gradle and Maven ○ incorporated in Spring Boot build plugins

Test-specific Runtime Hints ● A lot is already built-in! ● TestRuntimeHintsRegistrar ● register globally via META-INF/spring/aot.factories ● RuntimeHintsRegistrar ● register globally via META-INF/spring/aot.factories ● register locally on a test class via @ImportRuntimeHints ● Annotate test class with @Reflective or @RegisterReflectionForBinding

Implementing Custom AOT Testing Support ● ContextLoader: implement AotContextLoader ● AOT build-time processing ● AOT runtime execution support ● Spring Framework and Spring Boot context loaders implement AotContextLoader ● TestExecutionListener: implement AotTestExecutionListener ● to participate in AOT processing ● See SqlScriptsTestExecutionListener for an example

JUnit Support for Native Images ● @EnabledInNativeImage and @DisabledInNativeImage ○ JUnit Jupiter execution conditions ● Native Build Tools (NBT) support for JUnit Platform ● Explicit support for JUnit Jupiter and JUnit 4 ● Spring Boot 3 build tools ○ Gradle and Maven ○ Integration with NBT for testing support

Running Spring Integration Tests in Native Image ● Maven ○ ./mvnw -PnativeTest test ● Gradle ○ ./gradlew nativeTest ● Definitely do this before deploying a native image to production ● But this can take a considerable amount of time ● So you won’t do this multiple times a day ● Consider running tests in AOT mode on the JVM first

Disclaimer: Testing in AOT mode on JVM ● Not yet ready for prime time ○ in terms of developer experience (DX) ○ requires manual setup ● But still possible with both Maven and Gradle ○ Today I’ll show you how with Maven ● Can be useful to: ○ run tests in AOT mode on the JVM before running within a native image ○ debug failing tests first in AOT mode on the JVM

Mini Maven / Spring AOT Tutorial ● Generate AOT test sources ○ ./mvnw clean test spring-boot:process-test-aot ● Run tests in AOT mode on JVM ○ ./mvnw -Dspring.aot.enabled=true test ● Add generated sources as “test” source folder in IDE ○ target/spring-aot/test/sources/ ○ output directory can be same as for your test code ● Add CGLIB compiled classes to output classpath in IDE ● alternative: @Configuration(proxyBeanMethods = false)

Testing in AOT Mode ● Run test class with -Dspring.aot.enabled=true ● That’s it! ● You should see log output like: ● Loading ApplicationContext for AOT runtime for test class springio.service.ServiceTests ● Starting AOT-processed ServiceTests

Debugging in AOT Mode ● Find mapping from test class to AOT-optimized ApplicationContext ○ org.springframework.test.context.aot.AotTestContextInitializers__Generated ○ For example, ServiceTests__TestContext001_ApplicationContextInitializer ● Set breakpoint in ApplicationContextInitializer ● Debug test class with -Dspring.aot.enabled=true

DEMO TIME! 🤞

THANK YOU! Q&A Sam Brannen @sam_brannen