java.lang.IllegalStateException: Failed to transform class with name com.xxx.xxx. Reason: null

[DamonEvil]

maven version:

        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>2.28.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-api-mockito2</artifactId>
            <version>2.0.9</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-module-junit4</artifactId>
            <version>2.0.9</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.jacoco/org.jacoco.agent -->
        <dependency>
            <groupId>org.jacoco</groupId>
            <artifactId>org.jacoco.agent</artifactId>
            <version>${jacoco.version}</version>
            <classifier>runtime</classifier>
            <scope>test</scope>
        </dependency>

I will use the Be-tested class to replace the name of the class I tested for privacy purpose.And the Be-tested class extends a abstract class which implements an interface.

when I want to use PowerMock to mock the Be-tested Class's method, I add the annotation on the class

@RunWith(PowerMockRunner.class)
@PrepareForTest({Be-tested.class})

Then I start the test method, It runs failed Before executing any code in my test method with reason as follows:

java.lang.IllegalStateException: Failed to transform class with name com.xxx.xxx.xxx. Reason: null

	at org.powermock.core.classloader.javassist.JavassistMockClassLoader.defineAndTransformClass(JavassistMockClassLoader.java:119)
	at org.powermock.core.classloader.MockClassLoader.loadMockClass(MockClassLoader.java:174)
	at org.powermock.core.classloader.MockClassLoader.loadClassByThisClassLoader(MockClassLoader.java:102)
	at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass1(DeferSupportingClassLoader.java:147)
	at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass(DeferSupportingClassLoader.java:98)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:348)
	at sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:114)
	at sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:125)
	at sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49)
	at sun.reflect.annotation.AnnotationParser.parseSig(AnnotationParser.java:439)
	at sun.reflect.annotation.AnnotationParser.parseClassValue(AnnotationParser.java:420)
	at sun.reflect.annotation.AnnotationParser.parseClassArray(AnnotationParser.java:724)
	at sun.reflect.annotation.AnnotationParser.parseArray(AnnotationParser.java:531)
	at sun.reflect.annotation.AnnotationParser.parseMemberValue(AnnotationParser.java:355)
	at sun.reflect.annotation.AnnotationParser.parseAnnotation2(AnnotationParser.java:286)
	at sun.reflect.annotation.AnnotationParser.parseAnnotations2(AnnotationParser.java:120)
	at sun.reflect.annotation.AnnotationParser.parseAnnotations(AnnotationParser.java:72)
	at java.lang.Class.createAnnotationData(Class.java:3521)
	at java.lang.Class.annotationData(Class.java:3510)
	at java.lang.Class.getAnnotation(Class.java:3415)
	at org.junit.internal.MethodSorter.getDeclaredMethods(MethodSorter.java:52)
	at org.junit.internal.runners.TestClass.getAnnotatedMethods(TestClass.java:45)
	at org.junit.internal.runners.MethodValidator.validateTestMethods(MethodValidator.java:71)
	at org.junit.internal.runners.MethodValidator.validateStaticMethods(MethodValidator.java:44)
	at org.junit.internal.runners.MethodValidator.validateMethodsForDefaultRunner(MethodValidator.java:50)
	at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.validate(PowerMockJUnit44RunnerDelegateImpl.java:124)
	at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.<init>(PowerMockJUnit44RunnerDelegateImpl.java:86)
	at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl.<init>(PowerMockJUnit47RunnerDelegateImpl.java:42)
	at org.powermock.modules.junit4.internal.impl.PowerMockJUnit49RunnerDelegateImpl.<init>(PowerMockJUnit49RunnerDelegateImpl.java:25)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.createDelegatorFromClassloader(JUnit4TestSuiteChunkerImpl.java:165)
	at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.createDelegatorFromClassloader(JUnit4TestSuiteChunkerImpl.java:47)
	at org.powermock.tests.utils.impl.AbstractTestSuiteChunkerImpl.createTestDelegators(AbstractTestSuiteChunkerImpl.java:107)
	at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.<init>(JUnit4TestSuiteChunkerImpl.java:69)
	at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.<init>(AbstractCommonPowerMockRunner.java:36)
	at org.powermock.modules.junit4.PowerMockRunner.<init>(PowerMockRunner.java:34)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.junit.internal.builders.AnnotatedBuilder.buildRunner(AnnotatedBuilder.java:104)
	at org.junit.internal.builders.AnnotatedBuilder.runnerForClass(AnnotatedBuilder.java:86)
	at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:70)
	at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:37)
	at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:70)
	at org.junit.internal.requests.ClassRequest.createRunner(ClassRequest.java:28)
	at org.junit.internal.requests.MemoizingRequest.getRunner(MemoizingRequest.java:19)
	at org.junit.internal.requests.FilterRequest.getRunner(FilterRequest.java:36)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:50)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:911)
	at java.util.ArrayList$Itr.next(ArrayList.java:861)
	at javassist.CtClassType.instrument(CtClassType.java:1540)
	at org.powermock.core.transformers.javassist.InstrumentMockTransformer.transform(InstrumentMockTransformer.java:41)
	at org.powermock.core.transformers.javassist.AbstractJavaAssistMockTransformer.transform(AbstractJavaAssistMockTransformer.java:40)
	at org.powermock.core.transformers.support.DefaultMockTransformerChain.transform(DefaultMockTransformerChain.java:43)
	at org.powermock.core.classloader.MockClassLoader.transformClass(MockClassLoader.java:184)
	at org.powermock.core.classloader.javassist.JavassistMockClassLoader.defineAndTransformClass(JavassistMockClassLoader.java:102)
	... 56 more

It seems like ConcurrentModificationException. And I follow the exception caught by position at org.powermock.core.classloader.javassist.JavassistMockClassLoader.defineAndTransformClass(JavassistMockClassLoader.java:119)

it shows the exception is in class - CtClassType, method - instrument(ExprEditor editor)
when for loop methods . the first time methods‘ size is 10, and after editor.doit(this,minfo). methods'size plus 1 becoming 11, and the enhanced for loop throws a ConcurrentModificationException.

I wanna know why it is and how can I avoid this exception. Because except this class ,I cannot recurrent with my demo class which extends a abstract class and implements a normal interface.

Thanks you.