ClassCastException when using mockito & powermock

Question

when running a junit4 testcase in eclipse it works fine as a stand-alone app i get the following stack trace.

java.lang.ExceptionInInitializerError:
        at sun.reflect.GeneratedSerializationConstructorAccessor6.newInstance(Unknown Source)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
        at org.objenesis.instantiator.sun.SunReflectionFactoryInstantiator.newInstance(SunReflectionFactoryInstantiator.java:40)
        at org.objenesis.ObjenesisBase.newInstance(ObjenesisBase.java:59)
        at org.mockito.internal.creation.jmock.ClassImposterizer.createProxy(ClassImposterizer.java:128)
        at org.mockito.internal.creation.jmock.ClassImposterizer`enter code here`.imposterise(ClassImposterizer.java:63)
        at org.powermock.api.mockito.internal.mockcreation.MockCreator.createMethodInvocationControl(MockCreator.java:111)
        at org.powermock.api.mockito.internal.mockcreation.MockCreator.mock(MockCreator.java:60)
        at org.powermock.api.mockito.PowerMockito.mock(PowerMockito.java:143)
        at org.powermock.api.extension.listener.AnnotationEnabler.standardInject(AnnotationEnabler.java:84)
        at org.powermock.api.extension.listener.AnnotationEnabler.beforeTestMethod(AnnotationEnabler.java:51)
        at org.powermock.tests.utils.impl.PowerMockTestNotifierImpl.notifyBeforeTestMethod(PowerMockTestNotifierImpl.java:90)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:292)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.access$100(PowerMockJUnit47RunnerDelegateImpl.java:59)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner$LastRuleTestExecutorStatement.evaluate(PowerMockJUnit47RunnerDelegateImpl.java:148)
        at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:91)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:282)
        at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
        at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:207)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
        at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
        at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
        at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:118)
        at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:104)
        at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
        at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:53)
        at org.junit.runners.Suite.runChild(Suite.java:127)
        at org.junit.runners.Suite.runChild(Suite.java:26)
        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 org.junit.runner.JUnitCore.run(JUnitCore.java:138)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:117)
        at testcases.net.idt.debit.ratesvr.monitor.MonitorTest.main(MonitorTest.java:392)
Caused by: java.lang.ClassCastException: org.powermock.core.classloader.MockClassLoader cannot be cast to java.net.URLClassLoader

my test case uses the following annotaions

@RunWith(PowerMockRunner.class)
@PrepareForTest({Monitor.class, Client.class, java.net.URLClassLoader.class})
@PowerMockIgnore( {"javax.management.*", "java.lang.*", "java.security.*", "java.net.*" })

how do i tell it to ignore URLClasLoader?

Answer 1

the class to be mocked Monitor.class extended another class MonitorBase.class in that class there was a static initializer

static {
....
}

so when the Monitor.class was loaded, MonitorBase.class was instaniated before it could be "mocked" I removed the "extends MonitorBase" and created a Monitor interface for MonitorBase.class

that solved the problem