NPE trying to mock interface using mockito-core 2.0.43-beta

I was working with Vert.x (3.2.0) and noticed that I got a strange NullPointerException when upgrading mockito from 1.10.19 to the latest beta version of 2.0.43-beta.

It appears Mockito JUnit runner cannot initialize a mock of the io.vertx.ext.web.RoutingContext that is annotated with @Mock as in this simple code snippet:

package com.example;

import io.vertx.ext.web.RoutingContext;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class MockRoutingContextTest1 {

    @Mock
    public RoutingContext routingContext;

    @Test
    public void someTest() throws Exception {
        // Does nothing
    }
}

This gives the following stacktrace when trying to build (Java 8, Gradle 2.10):

org.mockito.exceptions.base.MockitoException: 
Mockito cannot mock this class: interface io.vertx.ext.web.RoutingContext

Mockito can only mock visible & non-final classes.
If you're not sure why you're getting this error, please report to the mailing list.

Underlying exception : java.lang.IllegalStateException: Error invoking java.lang.reflect.Method#getAnnotatedReturnType
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl$1.withBefores(JUnit45AndHigherRunnerImpl.java:27)
    at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:276)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37)
    at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.runTestClass(JUnitTestClassExecuter.java:105)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:56)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:64)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:50)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.messaging.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
    at org.gradle.messaging.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
    at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:106)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:360)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:54)
    at org.gradle.internal.concurrent.StoppableExecutorImpl$1.run(StoppableExecutorImpl.java:40)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalStateException: Error invoking java.lang.reflect.Method#getAnnotatedReturnType
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Dispatcher$ForJava8CapableVm$AnnotatedReturnType.resolve(TypeDescription.java:3175)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Delegator.asList(TypeDescription.java:3472)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfNonGenericType$ForLoadedType.getDeclaredAnnotations(TypeDescription.java:4226)
    at net.bytebuddy.implementation.attribute.AnnotationAppender$ForTypeAnnotations.apply(AnnotationAppender.java:718)
    at net.bytebuddy.implementation.attribute.AnnotationAppender$ForTypeAnnotations.onNonGenericType(AnnotationAppender.java:699)
    at net.bytebuddy.implementation.attribute.AnnotationAppender$ForTypeAnnotations.onNonGenericType(AnnotationAppender.java:413)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfNonGenericType.accept(TypeDescription.java:4093)
    at net.bytebuddy.implementation.attribute.MethodAttributeAppender$ForInstrumentedMethod.apply(MethodAttributeAppender.java:175)
    at net.bytebuddy.implementation.attribute.MethodAttributeAppender$Compound.apply(MethodAttributeAppender.java:482)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:564)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:500)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:3452)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1579)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:164)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:2508)
    at org.mockito.internal.creation.bytebuddy.MockBytecodeGenerator.generateMockClass(MockBytecodeGenerator.java:60)
    at org.mockito.internal.creation.bytebuddy.CachingMockBytecodeGenerator$CachedBytecodeGenerator.generate(CachingMockBytecodeGenerator.java:72)
    at org.mockito.internal.creation.bytebuddy.CachingMockBytecodeGenerator$CachedBytecodeGenerator.getOrGenerateMockClass(CachingMockBytecodeGenerator.java:64)
    at org.mockito.internal.creation.bytebuddy.CachingMockBytecodeGenerator.get(CachingMockBytecodeGenerator.java:27)
    at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.createProxyClass(ByteBuddyMockMaker.java:54)
    at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.createMock(ByteBuddyMockMaker.java:27)
    at org.mockito.internal.util.MockUtil.createMock(MockUtil.java:32)
    at org.mockito.internal.MockitoCore.mock(MockitoCore.java:55)
    at org.mockito.Mockito.mock(Mockito.java:1449)
    at org.mockito.internal.configuration.MockAnnotationProcessor.process(MockAnnotationProcessor.java:33)
    at org.mockito.internal.configuration.MockAnnotationProcessor.process(MockAnnotationProcessor.java:16)
    at org.mockito.internal.configuration.DefaultAnnotationEngine.createMockFor(DefaultAnnotationEngine.java:43)
    at org.mockito.internal.configuration.DefaultAnnotationEngine.process(DefaultAnnotationEngine.java:66)
    at org.mockito.internal.configuration.InjectingAnnotationEngine.processIndependentAnnotations(InjectingAnnotationEngine.java:71)
    at org.mockito.internal.configuration.InjectingAnnotationEngine.process(InjectingAnnotationEngine.java:55)
    at org.mockito.MockitoAnnotations.initMocks(MockitoAnnotations.java:108)
    ... 38 more
Caused by: java.lang.NullPointerException
    at sun.reflect.annotation.TypeAnnotationParser.mapTypeAnnotations(TypeAnnotationParser.java:356)
    at sun.reflect.annotation.AnnotatedTypeFactory$AnnotatedTypeBaseImpl.<init>(AnnotatedTypeFactory.java:139)
    at sun.reflect.annotation.AnnotatedTypeFactory.buildAnnotatedType(AnnotatedTypeFactory.java:65)
    at sun.reflect.annotation.TypeAnnotationParser.buildAnnotatedType(TypeAnnotationParser.java:79)
    at java.lang.reflect.Executable.getAnnotatedReturnType0(Executable.java:633)
    at java.lang.reflect.Method.getAnnotatedReturnType(Method.java:648)
    at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Dispatcher$ForJava8CapableVm$AnnotatedReturnType.resolve(TypeDescription.java:3171)
    ... 68 more

Looks like the offending line in RoutingContext might be:

  /**
   * Set the acceptable content type. Used by
   * @param contentType  the content type
   */
  void setAcceptableContentType(@Nullable String contentType);

Maybe that @Nullable annotation?

Switching back to the 1.x version of Mockito everything works fine again.

[thekingn0thing]

Hello @aschrijver

I’ve resolved the issue by adding testCompile 'io.vertx:vertx-codegen:3.2.1' to dependencies. Your guess is correct, Bytebuddy cannot find at runtime annotations @Nullableand @CacheReturn. Both annotation are located in this jar.

[raphw]

The issue number is JI-9030867. The problem is easy to reproduce without Byte Buddy or Mockito involved. Calling

RoutingContext.class.getDeclaredMethod("mountPoint").getAnnotatedReturnType();

without io.vertx:vertx-codegen:3.2.1 being visible to the class loader of RoutingContext causes the NullPointerException. A minimal reproduction can be created by compiling:

class Foo {
  public static void main(String[] args) throws Exception {
    Foo.class.getDeclaredMethod("sample").getAnnotatedReturnType();
  }
  @Bar Object sample() { return null; } 
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE_USE)
@interface Bar { }

and then running Foo after deleting Bar.class. The exception observed is:

Exception in thread “main” java.lang.NullPointerException at sun.reflect.annotation.TypeAnnotationParser.mapTypeAnnotations(TypeAnnotationParser.java:356) at sun.reflect.annotation.AnnotatedTypeFactory$AnnotatedTypeBaseImpl.<init>(AnnotatedTypeFactory.java:139) at sun.reflect.annotation.AnnotatedTypeFactory.buildAnnotatedType(AnnotatedTypeFactory.java:65) at sun.reflect.annotation.TypeAnnotationParser.buildAnnotatedType(TypeAnnotationParser.java:79) at java.lang.reflect.Executable.getAnnotatedReturnType0(Executable.java:633) at java.lang.reflect.Method.getAnnotatedReturnType(Method.java:648) at Foo.main(Foo.java:5)