This project is a reproducer project showcasing a problem in testing a Spring Boot Application when using ServletRegistrationBean and @EnableAsync and tests with different configuration contexts.
The error can be seen by running ./mvnw verify,
The first test runs OK. But the second one doesn't.
The error is:
2022-01-22 09:43:56.248 ERROR 19160 --- [ main] o.s.test.context.TestContextManager : Caught exception while allowing TestExecutionListener [org.springframework.boot.test.autoconfigure.SpringBootDependencyInjectionTestExecutionListener@6c8efde4] to prepare test instance [com.example.demo.DemoApplicationTests@4e2cdc51]
java.lang.IllegalStateException: Failed to load ApplicationContext
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:132) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:124) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:118) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:83) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.boot.test.autoconfigure.SpringBootDependencyInjectionTestExecutionListener.prepareTestInstance(SpringBootDependencyInjectionTestExecutionListener.java:43) ~[spring-boot-test-autoconfigure-2.6.3.jar:2.6.3]
at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:248) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.test.context.junit.jupiter.SpringExtension.postProcessTestInstance(SpringExtension.java:138) ~[spring-test-5.3.15.jar:5.3.15]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$8(ClassBasedTestDescriptor.java:363) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.executeAndMaskThrowable(ClassBasedTestDescriptor.java:368) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeTestInstancePostProcessors$9(ClassBasedTestDescriptor.java:363) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179) ~[na:na]
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[na:na]
at java.base/java.util.stream.StreamSpliterators$WrappingSpliterator.forEachRemaining(StreamSpliterators.java:310) ~[na:na]
at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:735) ~[na:na]
at java.base/java.util.stream.Streams$ConcatSpliterator.forEachRemaining(Streams.java:734) ~[na:na]
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[na:na]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeTestInstancePostProcessors(ClassBasedTestDescriptor.java:362) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$instantiateAndPostProcessTestInstance$6(ClassBasedTestDescriptor.java:283) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.instantiateAndPostProcessTestInstance(ClassBasedTestDescriptor.java:282) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$4(ClassBasedTestDescriptor.java:272) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at java.base/java.util.Optional.orElseGet(Optional.java:364) ~[na:na]
at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$testInstancesProvider$5(ClassBasedTestDescriptor.java:271) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.execution.TestInstancesProvider.getTestInstances(TestInstancesProvider.java:31) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$prepare$0(TestMethodTestDescriptor.java:102) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:101) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.prepare(TestMethodTestDescriptor.java:66) ~[junit-jupiter-engine-5.8.2.jar:5.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$prepare$2(NodeTestTask.java:123) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.prepare(NodeTestTask.java:123) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:90) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) ~[na:na]
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54) ~[junit-platform-engine-1.8.2.jar:1.8.2]
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:220) ~[junit-platform-launcher-1.3.1.jar:1.3.1]
at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:188) ~[junit-platform-launcher-1.3.1.jar:1.3.1]
at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:202) ~[junit-platform-launcher-1.3.1.jar:1.3.1]
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:181) ~[junit-platform-launcher-1.3.1.jar:1.3.1]
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128) ~[junit-platform-launcher-1.3.1.jar:1.3.1]
at org.apache.maven.surefire.junitplatform.JUnitPlatformProvider.invokeAllTests(JUnitPlatformProvider.java:150) ~[surefire-junit-platform-2.22.2.jar:2.22.2]
at org.apache.maven.surefire.junitplatform.JUnitPlatformProvider.invoke(JUnitPlatformProvider.java:124) ~[surefire-junit-platform-2.22.2.jar:2.22.2]
at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:384) ~[surefire-booter-2.22.2.jar:2.22.2]
at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:345) ~[surefire-booter-2.22.2.jar:2.22.2]
at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:126) ~[surefire-booter-2.22.2.jar:2.22.2]
at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:418) ~[surefire-booter-2.22.2.jar:2.22.2]
Caused by: org.springframework.context.ApplicationContextException: Failed to start bean 'webServerStartStop'; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat server
at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.15.jar:5.3.15]
at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:732) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:414) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:302) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:136) ~[spring-boot-test-2.6.3.jar:2.6.3]
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:99) ~[spring-test-5.3.15.jar:5.3.15]
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124) ~[spring-test-5.3.15.jar:5.3.15]
... 68 common frames omitted
Caused by: org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat server
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.start(TomcatWebServer.java:229) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.web.servlet.context.WebServerStartStopLifecycle.start(WebServerStartStopLifecycle.java:43) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.15.jar:5.3.15]
... 82 common frames omitted
Caused by: org.springframework.boot.web.server.WebServerException: Servlet [Test Servlet] in web application [] threw load() exception
at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedContext.load(TomcatEmbeddedContext.java:87) ~[spring-boot-2.6.3.jar:2.6.3]
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183) ~[na:na]
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[na:na]
at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:276) ~[na:na]
at java.base/java.util.TreeMap$ValueSpliterator.forEachRemaining(TreeMap.java:3215) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[na:na]
at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150) ~[na:na]
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596) ~[na:na]
at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedContext.lambda$deferredLoadOnStartup$0(TomcatEmbeddedContext.java:65) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedContext.doWithThreadContextClassLoader(TomcatEmbeddedContext.java:106) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedContext.deferredLoadOnStartup(TomcatEmbeddedContext.java:64) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.performDeferredLoadOnStartup(TomcatWebServer.java:305) ~[spring-boot-2.6.3.jar:2.6.3]
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.start(TomcatWebServer.java:216) ~[spring-boot-2.6.3.jar:2.6.3]
... 84 common frames omitted
Caused by: javax.servlet.ServletException: Servlet.init() for servlet [Test Servlet] threw exception
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1181) ~[tomcat-embed-core-9.0.56.jar:9.0.56]
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1013) ~[tomcat-embed-core-9.0.56.jar:9.0.56]
at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedContext.load(TomcatEmbeddedContext.java:82) ~[spring-boot-2.6.3.jar:2.6.3]
... 100 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'demoService' defined in file [/Users/filiphr/development/oss/spring-boot-test-problem/target/classes/com/example/rest/DemoService.class]: Initialization of bean failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class com.example.rest.DemoService: Common causes of this problem include using a final class or a non-visible class; nested exception is org.springframework.cglib.core.CodeGenerationException: java.lang.LinkageError-->loader 'app' attempted duplicate class definition for com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d. (com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d is in unnamed module of loader 'app')
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:628) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:953) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.15.jar:5.3.15]
at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:702) ~[spring-webmvc-5.3.15.jar:5.3.15]
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:578) ~[spring-webmvc-5.3.15.jar:5.3.15]
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:530) ~[spring-webmvc-5.3.15.jar:5.3.15]
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:170) ~[spring-webmvc-5.3.15.jar:5.3.15]
at javax.servlet.GenericServlet.init(GenericServlet.java:158) ~[tomcat-embed-core-9.0.56.jar:4.0.FR]
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1164) ~[tomcat-embed-core-9.0.56.jar:9.0.56]
... 102 common frames omitted
Caused by: org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class com.example.rest.DemoService: Common causes of this problem include using a final class or a non-visible class; nested exception is org.springframework.cglib.core.CodeGenerationException: java.lang.LinkageError-->loader 'app' attempted duplicate class definition for com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d. (com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d is in unnamed module of loader 'app')
at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:209) ~[spring-aop-5.3.15.jar:5.3.15]
at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:110) ~[spring-aop-5.3.15.jar:5.3.15]
at org.springframework.aop.framework.AbstractAdvisingBeanPostProcessor.postProcessAfterInitialization(AbstractAdvisingBeanPostProcessor.java:99) ~[spring-aop-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:455) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1808) ~[spring-beans-5.3.15.jar:5.3.15]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:620) ~[spring-beans-5.3.15.jar:5.3.15]
... 116 common frames omitted
Caused by: org.springframework.cglib.core.CodeGenerationException: java.lang.LinkageError-->loader 'app' attempted duplicate class definition for com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d. (com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d is in unnamed module of loader 'app')
at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:580) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:363) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.proxy.Enhancer.generate(Enhancer.java:585) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:110) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:108) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.internal.LoadingCache$2.call(LoadingCache.java:54) ~[spring-core-5.3.15.jar:5.3.15]
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
at org.springframework.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:61) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.internal.LoadingCache.get(LoadingCache.java:34) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:134) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:319) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:572) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.cglib.proxy.Enhancer.createClass(Enhancer.java:419) ~[spring-core-5.3.15.jar:5.3.15]
at org.springframework.aop.framework.ObjenesisCglibAopProxy.createProxyClassAndInstance(ObjenesisCglibAopProxy.java:57) ~[spring-aop-5.3.15.jar:5.3.15]
at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:206) ~[spring-aop-5.3.15.jar:5.3.15]
... 121 common frames omitted
Caused by: java.lang.LinkageError: loader 'app' attempted duplicate class definition for com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d. (com.example.rest.DemoService$$EnhancerBySpringCGLIB$$8972e13d is in unnamed module of loader 'app')
at java.base/java.lang.ClassLoader.defineClass0(Native Method) ~[na:na]
at java.base/java.lang.System$2.defineClass(System.java:2307) ~[na:na]
at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2439) ~[na:na]
at java.base/java.lang.invoke.MethodHandles$Lookup$ClassDefiner.defineClass(MethodHandles.java:2416) ~[na:na]
at java.base/java.lang.invoke.MethodHandles$Lookup.defineClass(MethodHandles.java:1843) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na]
at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:577) ~[spring-core-5.3.15.jar:5.3.15]
... 135 common frames omitted
When running on Java 11 this works fine.
When moving the DemoService and ExampleResource to the com.example.demo package and removing the bean from the DemoApplication the tests run OK as well (they do fail, but due to the assertion).