Mock WebClient object with Answers.RETURNS_DEEP_STUBS cannot stub .header() & .headers()

Description

When performing unit tests by mocking the WebClient of Spring Boot WebFlux with @Mock(answer = Answers.RETURNS_DEEP_STUBS), an issue was found that the return value was null when calling the .header() and .headers() methods.

Used dependencies

Zulu OpenJDK 17.0.2
spring-boot-starter-webflux:2.6.7
mockito-core:4.0.0
mockito-junit-jupiter:4.0.0

Codes

@Service
@RequiredArgsConstructor
public class WebClientService {

    private final WebClient webClient;
    private final WebClient.Builder webClientBuilder;

    public WebClientResponse request() {

        final ResponseEntity<WebClientResponse> response =
            webClient.get()
                     .uri("http://localhost:1234")
                     .header("a", "a") // comment out these line, it works
                     .retrieve()
                     .toEntity(WebClientResponse.class)
                     .block();

        return response.getBody();
    }
}

public record WebClientRequest() {}
public record WebClientResponse(HttpStatus httpStatus, String response) {}

@ExtendWith(MockitoExtension.class)
class WebClientServiceTest {

    @Mock(answer = Answers.RETURNS_DEEP_STUBS)
    private WebClient webClient;
    @Mock(answer = Answers.RETURNS_SELF)
    private WebClient.Builder webClientBuilder;
    @InjectMocks
    private WebClientService webClientService;

    @Test
    void test() {
        when(webClient.get()
                      .uri(anyString())
                      .header(anyString(), anyString()) // (any(), any()) also does not work
                      .retrieve()
                      .toEntity(WebClientResponse.class)
                      .block())
            .thenReturn(ResponseEntity.ok(new WebClientResponse(HttpStatus.OK,
                                                                HttpStatus.OK.getReasonPhrase())));

        final WebClientResponse response = webClientService.request();
        assertEquals(HttpStatus.OK, response.httpStatus());
    }
}

Errors

Cannot invoke "org.springframework.web.reactive.function.client.WebClient$RequestHeadersSpec.retrieve()" because the return value of "org.springframework.web.reactive.function.client.WebClient$RequestHeadersSpec.header(String, String[])" is null
java.lang.NullPointerException: Cannot invoke "org.springframework.web.reactive.function.client.WebClient$RequestHeadersSpec.retrieve()" because the return value of "org.springframework.web.reactive.function.client.WebClient$RequestHeadersSpec.header(String, String[])" is null
	at com.example.service.WebClientServiceTest.test(WebClientServiceTest.java:35)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
	at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
	at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
	at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
	at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
	at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
	at jdk.proxy1/jdk.proxy1.$Proxy2.stop(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
	at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
	at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
	at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)

Debugger screenshots

Additional info

There is only .header() example in the code, but .headers() also has the same NPE.
If I’m misunderstanding what @Mock(answer = Answers.RETURNS_DEEP_STUBS) is for, please comment.
If possible, I would appreciate it if you could point me to the exact code that needs to be fixed.
For reference, I tried to apply the latest mockito to see if it could be solved, but the following error occurred and the test could not be run.

    testImplementation("org.mockito:mockito-core:4.5.1")
    testImplementation("org.mockito:mockito-junit-jupiter:4.5.1")
    testImplementation("net.bytebuddy:byte-buddy-agent:1.12.10")

Could not initialize plugin: interface org.mockito.plugins.MockMaker (alternate: null)
java.lang.IllegalStateException: Could not initialize plugin: interface org.mockito.plugins.MockMaker (alternate: null)
	at org.mockito.internal.configuration.plugins.PluginLoader$1.invoke(PluginLoader.java:88)
	at jdk.proxy3/jdk.proxy3.$Proxy14.isTypeMockable(Unknown Source)
	at org.mockito.internal.util.MockUtil.typeMockabilityOf(MockUtil.java:33)
	at org.mockito.internal.util.MockCreationValidator.validateType(MockCreationValidator.java:22)
	at org.mockito.internal.creation.MockSettingsImpl.validatedSettings(MockSettingsImpl.java:250)
	at org.mockito.internal.creation.MockSettingsImpl.build(MockSettingsImpl.java:232)
	at org.mockito.internal.MockitoCore.mock(MockitoCore.java:94)
	at org.mockito.Mockito.mock(Mockito.java:1965)
	at org.mockito.internal.configuration.MockAnnotationProcessor.processAnnotationForMock(MockAnnotationProcessor.java:66)
	at org.mockito.internal.configuration.MockAnnotationProcessor.process(MockAnnotationProcessor.java:27)
	at org.mockito.internal.configuration.MockAnnotationProcessor.process(MockAnnotationProcessor.java:24)
	at org.mockito.internal.configuration.IndependentAnnotationEngine.createMockFor(IndependentAnnotationEngine.java:44)
	at org.mockito.internal.configuration.IndependentAnnotationEngine.process(IndependentAnnotationEngine.java:72)
	at org.mockito.internal.configuration.InjectingAnnotationEngine.processIndependentAnnotations(InjectingAnnotationEngine.java:73)
	at org.mockito.internal.configuration.InjectingAnnotationEngine.process(InjectingAnnotationEngine.java:47)
	at org.mockito.MockitoAnnotations.openMocks(MockitoAnnotations.java:81)
	at org.mockito.internal.framework.DefaultMockitoSession.<init>(DefaultMockitoSession.java:43)
	at org.mockito.internal.session.DefaultMockitoSessionBuilder.startMocking(DefaultMockitoSessionBuilder.java:83)
	at org.mockito.junit.jupiter.MockitoExtension.beforeEach(MockitoExtension.java:153)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeBeforeEachCallbacks$2(TestMethodTestDescriptor.java:163)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeBeforeMethodsOrCallbacksUntilExceptionOccurs$6(TestMethodTestDescriptor.java:199)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeMethodsOrCallbacksUntilExceptionOccurs(TestMethodTestDescriptor.java:199)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeEachCallbacks(TestMethodTestDescriptor.java:162)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:129)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
	at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
	at jdk.proxy1/jdk.proxy1.$Proxy2.stop(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
	at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
	at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
	at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
	Suppressed: java.lang.NullPointerException: Cannot invoke "java.util.Set.forEach(java.util.function.Consumer)" because the return value of "org.junit.jupiter.api.extension.ExtensionContext$Store.remove(Object, java.lang.Class)" is null
		at org.mockito.junit.jupiter.MockitoExtension.afterEach(MockitoExtension.java:184)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeAfterEachCallbacks$12(TestMethodTestDescriptor.java:257)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeAllAfterMethodsOrCallbacks$13(TestMethodTestDescriptor.java:273)
		at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeAllAfterMethodsOrCallbacks$14(TestMethodTestDescriptor.java:273)
		at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeAllAfterMethodsOrCallbacks(TestMethodTestDescriptor.java:272)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeAfterEachCallbacks(TestMethodTestDescriptor.java:256)
		at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:141)
		... 61 more
Caused by: java.lang.IllegalStateException: Internal problem occurred, please report it. Mockito is unable to load the default implementation of class that is a part of Mockito distribution. Failed to load interface org.mockito.plugins.MockMaker
	at org.mockito.internal.configuration.plugins.DefaultMockitoPlugins.create(DefaultMockitoPlugins.java:85)
	at org.mockito.internal.configuration.plugins.DefaultMockitoPlugins.getDefaultPlugin(DefaultMockitoPlugins.java:59)
	at org.mockito.internal.configuration.plugins.PluginLoader.loadPlugin(PluginLoader.java:79)
	at org.mockito.internal.configuration.plugins.PluginLoader.loadPlugin(PluginLoader.java:54)
	at org.mockito.internal.configuration.plugins.PluginRegistry.<init>(PluginRegistry.java:28)
	at org.mockito.internal.configuration.plugins.Plugins.<clinit>(Plugins.java:22)
	at org.mockito.internal.MockitoCore.<clinit>(MockitoCore.java:77)
	at org.mockito.Mockito.<clinit>(Mockito.java:1614)
	at org.mockito.junit.jupiter.MockitoExtension.beforeEach(MockitoExtension.java:149)
	... 67 more
Caused by: java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at org.mockito.internal.configuration.plugins.DefaultMockitoPlugins.create(DefaultMockitoPlugins.java:83)
	... 75 more
Caused by: org.mockito.exceptions.base.MockitoInitializationException: 
It seems like you are running Mockito with an incomplete or inconsistent class path. Byte Buddy could not be loaded.

Byte Buddy is available on Maven Central as 'net.bytebuddy:byte-buddy' with the module name 'net.bytebuddy'.
For the inline mock maker, 'net.bytebuddy:byte-buddy-agent' with the module name 'net.bytebuddy.agent' is also required.
Normally, your IDE or build tool (such as Maven or Gradle) should take care of your class path completion but 
	at app//org.mockito.internal.exceptions.Reporter.missingByteBuddyDependency(Reporter.java:1127)
	at app//org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.<init>(ByteBuddyMockMaker.java:31)
	... 81 more
Caused by: java.lang.NoClassDefFoundError: net/bytebuddy/utility/GraalImageCode
	at org.mockito.internal.creation.bytebuddy.SubclassInjectionLoader.<init>(SubclassInjectionLoader.java:34)
	at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.<init>(SubclassByteBuddyMockMaker.java:33)
	at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.<init>(ByteBuddyMockMaker.java:29)
	... 81 more
Caused by: java.lang.ClassNotFoundException: net.bytebuddy.utility.GraalImageCode
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
	... 84 more

Issue Analytics

State:
Created a year ago
Reactions:1
Comments:7 (1 by maintainers)

Top GitHub Comments

2reactions

akutscheracommented, May 17, 2022

Well, I think you confused one little thing: uri() always returns a mocked object, therefore you can call uri().header() and also uri().retrieve() And the fact that the former returns null while the latter returns an mocked object can be explained because the methods have different return types.

Also, keep in mind that uri() and header() are methods in two different (sub-)interfaces, therefore the S is not the same type.

I am just a user of mockito. If I wanted to improve this I would start by looking at this test because that is an example where the Iterable type (Article) gets lost.

2reactions

akutscheracommented, May 13, 2022

I find this interesting. It looks like because of type erasure somewhere in the stack mockito does not know what type of object it should return and therefore returns null (see here

I can reproduce this with a smaller test

@ExtendWith(MockitoExtension.class)
public class SimpleTest {

    public interface TopLevel<T> {
        T getT();
        List<String> getList();
    }

    @Mock // (answer = Answers.RETURNS_DEEP_STUBS) -- fails with and without
    private TopLevel<List<String>> topLevel;

    @Test
    void test() {
        assertThat( topLevel.getList() ).isEmpty(); // works as expected
        assertThat( topLevel.getT() ).isNotNull(); // fails
    }
}

It seems that the information that we have a List<String> as the generic for topLevel is lost somewhere. There is the workaround of mocking each step instead of using RETURNS_DEEP_STUBS, even though I agree this leads to a test that is difficult to read/maintain.