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POMockito + PowerMock LinkageError while mocking system class
 

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  1. POMockito + PowerMock LinkageError while mocking system class
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    <p>I've got such a code snippet:</p> <pre><code>@RunWith(PowerMockRunner.class) @PrepareForTest({Thread.class}) public class AllMeasuresDataTest { @Before public void setUp() throws Exception { } @Test public void testGetMeasures() { AllMeasuresData measure = new AllMeasuresData(); assertEquals(measure.getMeasures(), null); HashMap&lt;String, Measure&gt; map = new HashMap&lt;String, Measure&gt;(); measure.setMeasures(map); assertEquals(measure.getMeasures(), map); measure.setMeasures(null); assertEquals(measure.getMeasures(), null); } @Test public void testAllMeasuresData() throws IOException { ClassLoader loader = PowerMockito.mock(ClassLoader.class); Thread threadMock = PowerMockito.mock(Thread.class); Vector&lt;URL&gt; vec = new Vector&lt;URL&gt;(); Mockito.when(loader.getResources("measure")).thenReturn(vec.elements()); Mockito.when(threadMock.getContextClassLoader()).thenReturn(loader); PowerMockito.mockStatic(Thread.class); Mockito.when(Thread.currentThread()).thenReturn(threadMock); ... } } </code></pre> <p>While running this tests I got:</p> <pre><code>java.lang.LinkageError: loader constraint violation: loader (instance of org/powermock/core/classloader/MockClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:791) at java.lang.ClassLoader.defineClass(ClassLoader.java:634) at org.powermock.core.classloader.MockClassLoader.loadUnmockedClass(MockClassLoader.java:201) at org.powermock.core.classloader.MockClassLoader.loadModifiedClass(MockClassLoader.java:149) at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass(DeferSupportingClassLoader.java:67) at java.lang.ClassLoader.loadClass(ClassLoader.java:356) at org.codecover.instrumentation.java.measurement.ProtocolImpl.initializeMBean(ProtocolImpl.java:247) at org.codecover.instrumentation.java.measurement.ProtocolImpl.&lt;init&gt;(ProtocolImpl.java:237) at org.codecover.instrumentation.java.measurement.ProtocolImpl.getInstance(ProtocolImpl.java:185) at measure.CodeCoverCoverageCounter$6ya5ud0ow79ijrr1dvjrp4nxx60qhxeua02ta2fzpmb1d.&lt;clinit&gt;(MeasureCalculatorsHolder.java:146) at measure.MeasureCalculatorsHolder.&lt;clinit&gt;(MeasureCalculatorsHolder.java:17) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:188) at javassist.runtime.Desc.getClassObject(Desc.java:43) at javassist.runtime.Desc.getClassType(Desc.java:152) at javassist.runtime.Desc.getType(Desc.java:122) at javassist.runtime.Desc.getType(Desc.java:78) at algorithm.AllMeasuresDataTest.testGetMeasures(AllMeasuresDataTest.java:26) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:312) at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86) at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:296) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit49RunnerDelegateImpl$PowerMockJUnit49MethodRunner.executeTestInSuper(PowerMockJUnit49RunnerDelegateImpl.java:116) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit49RunnerDelegateImpl$PowerMockJUnit49MethodRunner.executeTest(PowerMockJUnit49RunnerDelegateImpl.java:77) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:284) at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84) at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:209) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:148) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:122) at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34) at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:120) at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:101) 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.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.codecover.juniteclipse.runner.EclipseTestRunner.main(EclipseTestRunner.java:40) </code></pre> <p>Do you know how can I prevent this? I maybe there is another way to mock such a piece of code:</p> <pre><code>ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); ... Enumeration&lt;URL&gt; resources = classLoader.getResources(path); </code></pre>
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    1. PTQuestion
    1. USKrease
    1. USWojciech Reszelewski
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    1. COWhat is it you're trying to mock? And why?
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      1. POMockito + PowerMock LinkageError while mocking system class
      1. USNilsH
    2. COFirst test is getters and setters test, I'm calling constructor there (and there the exception occurs). The second one is constructor test. I want to get control of what resources enumeration contains in third code snippet.
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      1. POMockito + PowerMock LinkageError while mocking system class
      1. USWojciech Reszelewski
    3. COFirst of all, it looks to me that your tests are very tightly coupled to your implementation. By experience, this will lead to fragile tests. Preferrably, you want to think "black box" when writing your tests. "What is this piece of code supposed to do", rather than "How is this piece of code doing it". Second, I think you'd be better off just creating a set of resources and let the Java runtime deal with the classloading itself.
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      1. POMockito + PowerMock LinkageError while mocking system class
      1. USNilsH
 

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