Mockito cannot mock this class

I am attempting to mock a public class, however when doing so, Mockito throws an Mockito cannot mock this class exception.

Class I wish to mock: https://github.com/scribejava/scribejava/blob/master/scribejava-core/src/main/java/com/github/scribejava/core/builder/ServiceBuilder.java

Test code:

package xyz.jacobclark.adapter;

import com.github.scribejava.apis.TwitterApi;
import com.github.scribejava.core.builder.ServiceBuilder;
import com.github.scribejava.core.model.OAuth1RequestToken;
import com.github.scribejava.core.oauth.OAuth10aService;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;

import java.io.IOException;

import static org.hamcrest.Matchers.is;
import static org.hamcrest.core.IsInstanceOf.any;

@RunWith(MockitoJUnitRunner.class)
public class TwitterOAuthAdapterTest {
    @Mock
    ServiceBuilder serviceBuilder;

    @Test
    public void getRequestTokenShouldReturnAValidRequestToken() throws IOException {
        class TwitterOAuthAdapter {
            private final OAuth10aService service;

            public TwitterOAuthAdapter(ServiceBuilder serviceBuilder){
                this.service = serviceBuilder
                    .apiKey("")
                    .apiSecret("")
                    .build(TwitterApi.instance());
            }

            public OAuth1RequestToken getRequestToken() throws IOException {
                return this.service.getRequestToken();
            }
        }

        TwitterOAuthAdapter oAuthAdapter = new TwitterOAuthAdapter(serviceBuilder);
        Assert.assertThat(oAuthAdapter.getRequestToken(), is(any(OAuth1RequestToken.class)));
    }
}

Full stacktrace:

xyz.jacobclark.adapter.TwitterOAuthAdapterTest

org.mockito.exceptions.base.MockitoException: 
Mockito cannot mock this class: class com.github.scribejava.core.builder.ServiceBuilder.

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


Java               : 1.8
JVM vendor name    : Oracle Corporation
JVM vendor version : 25.0-b70
JVM name           : Java HotSpot(TM) 64-Bit Server VM
JVM version        : 1.8.0-b132
JVM info           : mixed mode
OS name            : Mac OS X
OS version         : 10.11.3


Underlying exception : java.lang.IllegalArgumentException: object is not an instance of declaring class

	at org.mockito.internal.runners.SilentJUnitRunner$1.withBefores(SilentJUnitRunner.java:29)
	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$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.mockito.internal.runners.SilentJUnitRunner.run(SilentJUnitRunner.java:39)
	at org.mockito.internal.runners.StrictRunner.run(StrictRunner.java:39)
	at org.mockito.junit.MockitoJUnitRunner.run(MockitoJUnitRunner.java:103)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:117)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:42)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:262)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:84)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: java.lang.IllegalArgumentException: object is not an instance of declaring class
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$ForTypeArgument.resolve(TypeDescription.java:3843)
	at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Delegator$Chained.resolve(TypeDescription.java:3468)
	at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$ForTypeArgument.resolve(TypeDescription.java:3803)
	at net.bytebuddy.description.type.TypeDescription$Generic$AnnotationReader$Delegator.asList(TypeDescription.java:3439)
	at net.bytebuddy.description.type.TypeDescription$Generic$OfWildcardType$ForLoadedType.getDeclaredAnnotations(TypeDescription.java:4748)
	at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onWildcard(TypeDescription.java:680)
	at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onWildcard(TypeDescription.java:663)
	at net.bytebuddy.description.type.TypeDescription$Generic$OfWildcardType.accept(TypeDescription.java:4656)
	at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onParameterizedType(TypeDescription.java:691)
	at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing.onParameterizedType(TypeDescription.java:663)
	at net.bytebuddy.description.type.TypeDescription$Generic$OfParameterizedType.accept(TypeDescription.java:4998)
	at net.bytebuddy.description.type.TypeList$Generic$AbstractBase.accept(TypeList.java:249)
	at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$TypeVariableErasing$RetainedTypeVariable.getUpperBounds(TypeDescription.java:832)
	at net.bytebuddy.description.type.TypeDescription$Generic$OfTypeVariable.asErasure(TypeDescription.java:5373)
	at net.bytebuddy.description.method.MethodDescription$AbstractBase.asTypeToken(MethodDescription.java:701)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default$Key$Harmonized.of(MethodGraph.java:881)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default$Key$Store.registerTopLevel(MethodGraph.java:1074)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.doAnalyze(MethodGraph.java:588)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.analyze(MethodGraph.java:548)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.analyzeNullable(MethodGraph.java:567)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.doAnalyze(MethodGraph.java:581)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$Default.compile(MethodGraph.java:521)
	at net.bytebuddy.dynamic.scaffold.MethodGraph$Compiler$AbstractBase.compile(MethodGraph.java:442)
	at net.bytebuddy.dynamic.scaffold.MethodRegistry$Default.prepare(MethodRegistry.java:480)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:160)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:153)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:2568)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:2670)
	at org.mockito.internal.creation.bytebuddy.SubclassBytecodeGenerator.mockClass(SubclassBytecodeGenerator.java:84)
	at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator$CachedBytecodeGenerator.getOrGenerateMockClass(TypeCachingBytecodeGenerator.java:91)
	at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator.mockClass(TypeCachingBytecodeGenerator.java:38)
	at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMockType(SubclassByteBuddyMockMaker.java:67)
	at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMock(SubclassByteBuddyMockMaker.java:38)
	at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.createMock(ByteBuddyMockMaker.java:26)
	at org.mockito.internal.util.MockUtil.createMock(MockUtil.java:35)
	at org.mockito.internal.MockitoCore.mock(MockitoCore.java:63)
	at org.mockito.Mockito.mock(Mockito.java:1637)
	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:39)
	at org.mockito.internal.configuration.DefaultAnnotationEngine.process(DefaultAnnotationEngine.java:63)
	at org.mockito.internal.configuration.InjectingAnnotationEngine.processIndependentAnnotations(InjectingAnnotationEngine.java:59)
	at org.mockito.internal.configuration.InjectingAnnotationEngine.process(InjectingAnnotationEngine.java:43)
	at org.mockito.MockitoAnnotations.initMocks(MockitoAnnotations.java:67)
	... 23 more


Test ignored.
Process finished with exit code 255

Even though it's not specifically answering the question (question is Java 8), I came here via Google. Using Java 11, I solved this issue by including the following dependency in build.gradle:

compile group: 'org.mockito', name: 'mockito-core', version: '2.22.0'

as discussed here

It is because of Java/Mockito compatibility. For example, if you are using Java 11 with Mockito 2.17.0, it will throw the same error (Upgrading to Mockito 2.22.0 or later will solve it). Aside from digging into their release artifact on Github, I am yet to see a comprehensive document that spells out the compatibility matrix. Here is a helpful compatibility Matrix (based on quick test)

• Mockito * - 2.17.0 => Java 8

> (footnote: * - dont know how far back)

• Mockito 2.18.0 - 3.2.4 => Java 11

Had same issue. When I updated my Java JDK version to 1.8.0_131 the error disappeared.

I had the same issue. I tried everything that is listed on stack overflow i.e

• updated JDK version
• updated Maven
• Made ByteBuddy and Mockito to use compatible versions.
• cleared cache
• use latest mockito versions etc

and this : https://github.com/mockito/mockito/issues/1606.

But nothing worked for me.

I cleared all the cache and then reinstalled Android studio which fixed the issue.

Probably just clearing all the caches that Android Studio uses could have solved it too.

I had the same issue.

my jdk version is 11.0.4+10-LTS.

I use org.springframework.boot:spring-boot-starter-parent:2.0.7.RELEASE

I upgrade Mockito to 3.3.0

The exception still happen.

Then I did this:

1. exclusion mockito-core from spring-boot-starter-test

2. add below to pom file

       <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>3.3.0</version>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>net.bytebuddy</groupId>
                    <artifactId>byte-buddy</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>net.bytebuddy</groupId>
                    <artifactId>byte-buddy-agent</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>net.bytebuddy</groupId>
            <artifactId>byte-buddy</artifactId>
            <version>1.10.5</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>net.bytebuddy</groupId>
            <artifactId>byte-buddy-agent</artifactId>
            <version>1.10.5</version>
            <scope>test</scope>
        </dependency>

When I examined my Java-8 project's dependency tree I found that spring-boot-starter-test was using Mockito 2.15.0. Fixed by excluding that transitive Mockito dependency and re-adding it explicitly with version 2.23.4 (and re-build if not done automatically). Snippet of my maven POM:

<dependencies>
...
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-core</artifactId>
    <version>2.23.4</version>
</dependency>
</dependencies>

If using gradle it will look something like:

dependencies {
    ...
    def withoutMockito = {
        exclude group: 'org.mockito', module: 'mockito-core'
    }
    testImplementation "org.springframework.boot:spring-boot-starter-test:2.0.2-RELEASE", withoutMockito
    testImplementation "org.mockito:mockito-core:2.23.4"
 }

File -> Invalidate Caches / Restart

My class was public and non-final. This did the trick.

Update JDK, the error fixed when I've changed JDk 1.8 to 11, also I added this

@Rule
 public MockitoRule rule = MockitoJUnit.rule();

It's about 'Tells Mockito to create the mocks based on the @Mock annotation'

For me the issue was that the classes needed to be open.

I am using the:

@Mock lateinit var mock: ClassUnderTest

method of mocking.

For me, adding this dependency fixed the issue

androidTestImplementation "org.mockito:mockito-android:${versions.mockito}"

Make sure jdk version is selected correctly while running junit via Run As -> Run Configuration -> JRE tab.

I had the same issue after I update to new java version with OpenJ9 JVM, now I am using HotSpot JVM. I don't have this issue anymore

I had the same issue when I downgrade from JDK 13 to 1.8 error disappears. I think Mockito versions is not compatible with version 13.

I was facing same issue in my Android Studio.

Just upgrading of org.mockito:mockito-core from 2.18.3 to 2.19.0 ( Latest as of now) solved my issue.

I had the same issues.
My dependencies:

• spring-boot-parent:2.0.5.RELEASE
• org.testcontainers:1.16.3

I needed to start the app on Apple M1 with JVM 11

My tests failed with some issue.

I found in logs what used ~[mockito-core-2.15.0.jar:na]

After read the topic, I added one lib for fix my issue

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>2.18.0</version>
            <scope>test</scope>
        </dependency>

And for start testcontainers on Apple M1 is used fresh JNA

        <dependency>
            <groupId>net.java.dev.jna</groupId>
            <artifactId>jna</artifactId>
            <version>5.10.0</version>
            <scope>test</scope>
        </dependency>

in android studio i got this error and i cleaned the project and restarted the IDE to fix it.