Mockito object is not an instance of declaring class

Question

I haven't touched Mockito for a while, and I have never used it extensively. But today in some new code I wanted to use best practices so I pulled out mockito-core 2.0.54-beta using the following Java version:

java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)

I needed an instance of this interface for testing:

https://bitbucket.org/globalmentor/rincl/src/bf0e8875a1bae16247dd904e0b8bc067c9f8abc9/src/main/java/io/rincl/ResourceI18nConcern.java

public interface ResourceI18nConcern extends Concern {

    public Locale getLocale(@Nonnull Locale.Category category);

    public void setLocale(@Nonnull Locale.Category category, @Nonnull Locale locale);

    public default void setLocale(@Nonnull Locale locale) {...}

    public Resources getResources(@Nonnull final Class<?> contextClass) throws ResourceConfigurationException;

}

That interface extends this one (just an empty marker interface):

https://bitbucket.org/globalmentor/csar/src/125b837e9936ddb8d6340fa99b6b5da872d1e6e5/src/main/java/io/csar/Concern.java

In my test I tried to do this simple thing:

final ResourceI18nConcern defaultConcern=mock(ResourceI18nConcern.class);

I get the following stack trace:

org.mockito.exceptions.base.MockitoException:
Mockito cannot mock this class: interface io.rincl.ResourceI18nConcern

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.IllegalArgumentException: object is not an instance of declaring class
    at io.rincl.RinclTest.defaultConcernRinclGetLocaleIsConcernLocale(RinclTest.java:91)
    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:483)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    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$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$ForTypeArgument.resolve(TypeDescription.java:3875)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Delegator$Chained.resolve(TypeDescription.java:3501)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$ForTypeArgument.resolve(TypeDescription.java:3834)
    at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Delegator.asList(TypeDescription.java:3477)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfWildcardType$ForLoadedType.getDeclaredAnnotations(TypeDescription.java:4771)
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onWildcard(TypeDescription.java:676)
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onWildcard(TypeDescription.java:659)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfWildcardType.accept(TypeDescription.java:4679)
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onParameterizedType(TypeDescription.java:687)
    at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onParameterizedType(TypeDescription.java:659)
    at net.bytebuddy.description.type.TypeDescription$Generic$OfParameterizedType.accept(TypeDescription.java:5021)
    at net.bytebuddy.description.type.TypeDescription$Generic$LazyProjection.accept(TypeDescription.java:5794)
    at net.bytebuddy.description.method.ParameterDescription$TypeSubstituting.getType(ParameterDescription.java:866)
    at net.bytebuddy.description.method.ParameterList$AbstractBase.asTypeList(ParameterList.java:85)
    at net.bytebuddy.description.method.MethodDescription$AbstractBase.asTypeToken(MethodDescription.java:635)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default$Key$Harmonized.of(MethodGraph.java:862)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default$Key$Store.registerTopLevel(MethodGraph.java:1059)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.doAnalyze(MethodGraph.java:569)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.analyze(MethodGraph.java:529)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.doAnalyze(MethodGraph.java:565)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.compile(MethodGraph.java:502)
    at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$AbstractBase.compile(MethodGraph.java:423)
    at net.bytebuddy.dynamic.scaffold.MethodRegistry$Default.prepare(MethodRegistry.java:489)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:153)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:2564)
    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:54)
    at org.mockito.Mockito.mock(Mockito.java:1443)
    at org.mockito.Mockito.mock(Mockito.java:1356)
    ... 26 more

Am I doing something wrong? This seemed to me as if it should be straightforward.

To reproduce this problem, clone https://bitbucket.org/globalmentor/rincl.git and check out commit 2f88d7c5e5ac17b6d316ed54c12cb7b447b7d6ac. Then try to run the following test:

import static org.junit.Assert.*;
import static org.hamcrest.Matchers.*;
import static org.mockito.Mockito.*;
import java.util.Locale;
import java.util.Locale.Category;
import org.junit.*;

public class RinclTest {
    @Test
    public void defaultConcernRinclGetLocaleIsConcernLocale() {
        final ResourceI18nConcern defaultConcern=mock(ResourceI18nConcern.class);
    }
}

Answer 1

Your Java runtime version is from March 2014; plenty of bugs have been fixed in the VM ever since and you should really upgrade. I am 99% sure that this problem is related to type annotations (@NonNull) which were introduced in this version for the first time in this exact release. I am sure that your problem will go away if you upgrade your VM.

I can successfully execute your proposed test with a recent build of the HotSpot VM.

Answer 2

Had the same issue with my project and used the Rincl project above to confirm I was having the same issue. Using JDK 1.8.0_11 on Mac the reported errors were the same as Garret. Updating to version JDK 1.8.0_181 I ran the Rincl test with NO errors. Apparently Mockito is using the latest of the JDK 1.8.0.