Mockito 2 cannot mock kohsuke/github-api classes

A user (Adam) on the mailing list wasn’t sure if he misused mockito. So he reached us via the mailing-list.

Hi guys, a super simple test that creates a new mock of a public non-final class org.kohsuke.github.GHIssue from https://github.com/kohsuke/github-api version 1.77, source https://github.com/kohsuke/github-api/blob/github-api-1.77/src/main/java/org/kohsuke/github/GHIssue.java fails with:

mock(GHIssue.class);

org.mockito.exceptions.base.MockitoException: 
Mockito cannot mock this class: class org.kohsuke.github.GHIssue.

Mockito can only 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 : 25.101-b13
JVM name           : Java HotSpot(TM) 64-Bit Server VM
JVM version        : 1.8.0_101-b13
JVM info           : mixed mode
OS name            : Mac OS X
OS version         : 10.11.6


Underlying exception : java.lang.IllegalArgumentException: Cannot cast to primitive type: void

    at com.siemion.mockito.AppTest.test(AppTest.java:12)
    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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.lang.IllegalArgumentException: Cannot cast to primitive type: void
    at net.bytebuddy.implementation.bytecode.assign.TypeCasting.to(TypeCasting.java:39)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$AccessBridgeWrapper.apply(TypeWriter.java:1100)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:3802)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1618)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:172)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:153)
    at net.bytebuddy.dynamic.DynamicType$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:80)
    at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator$CachedBytecodeGenerator.getOrGenerateMockClass(TypeCachingBytecodeGenerator.java:87)
    at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator.mockClass(TypeCachingBytecodeGenerator.java:34)
    at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMockType(SubclassByteBuddyMockMaker.java:64)
    at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMock(SubclassByteBuddyMockMaker.java:35)
    at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.createMock(ByteBuddyMockMaker.java:22)
    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:1629)
    at org.mockito.Mockito.mock(Mockito.java:1542)
    ... 27 more

Or

mock(GHRepository.class);

java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    org/kohsuke/github/GHRepository$MockitoMock$667330966.getId()Ljava/lang/String; @4: checkcast
  Reason:
    Type integer (current frame, stack[0]) is not assignable to 'java/lang/Object'
  Current Frame:
    bci: @4
    flags: { }
    locals: { 'org/kohsuke/github/GHRepository$MockitoMock$667330966' }
    stack: { integer }
  Bytecode:
    0x0000000: 2ab6 003d c000 2eb0                    


    at sun.reflect.GeneratedSerializationConstructorAccessor1.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.objenesis.instantiator.sun.SunReflectionFactoryInstantiator.newInstance(SunReflectionFactoryInstantiator.java:45)
    at org.objenesis.ObjenesisBase.newInstance(ObjenesisBase.java:73)
    at org.mockito.internal.creation.instance.ObjenesisInstantiator.newInstance(ObjenesisInstantiator.java:14)

Related classes declaration

    <dependency>
      <groupId>org.kohsuke</groupId>
      <artifactId>github-api</artifactId>
      <version>1.77</version>
    </dependency>

---

After investigation on the project created by Adam Siemon here. I’ve reproduced the issue you are seeing with mockito 2.2.3 (bb 1.4.26) and 2.2.5 (bb 1.4.33), regardless of the JDK version. It seems related to how kohsuke/github-api generates bridge method in the byte code for backward compatibility ; this seems highly unusual, it may produce valid bytecode but with unmet bytecode patterns for mockito / bytebuddy. For reference the tool is called bridge-method-injector, more on the website

The classes you are mentioning are modified by this tool :

• GHIssues annotated by @WithBridgeMethods(void.class)
• GHRepository that inherits GHObject which also annotated by @WithBridgeMethods(value=String.class, adapterMethod="intToString")

It works with 1.10.19 because CGLIB is far less intelligent regarding bridge methods.

[raphw]

I understand the general intend to retain backwards compatibility but this is a general problem in Java and the hack might seem intelligent in the beginning but it is really problematic and might also confuse reflection. It would work much better if it was only used for final types.

I am glad I find these things out, encountering these issues makes Byte Buddy better in the long run 😉

[bric3]

no hurry 😉