I have a mockito junit's test using the command below. The variable serviceTask is an Interface's instancie called ServiceTask. I'm using a @Mock in the declarection
Declaraction:
@Mock
private ServiceTask
Command Line:
Mockito.when(serviceTask.getTask(Mockito.anyLong())).thenReturn(new Task());
Stack Trace:
java.lang.NullPointerException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:90) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55) at java.lang.reflect.Method.invoke(Method.java:508) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.mockito.internal.runners.DefaultInternalRunner$1$1.evaluate(DefaultInternalRunner.java:54) at org.junit.rules.ExpectedException$ExpectedExceptionStatement.evaluate(ExpectedException.java:239) at org.junit.rules.RunRules.evaluate(RunRules.java:20) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) 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.DefaultInternalRunner$1.run(DefaultInternalRunner.java:99) at org.mockito.internal.runners.DefaultInternalRunner.run(DefaultInternalRunner.java:105) at org.mockito.internal.runners.StrictRunner.run(StrictRunner.java:40) at org.mockito.junit.MockitoJUnitRunner.run(MockitoJUnitRunner.java:163) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)
The only reason for NPE if it happens at the line of code you mentioned above is serviceTask is null.
If you're not using the correct test runner which can help you to initialise the mock instance, then you can actually initialise them manually in your setUp method by using MockitoAnnotations.initMocks(this);
But if you already did so or used the correct test runner, then probably you linked to a wrong line of code. Try to debug yourself again.
Your stack trace doesn't look like it caused from your linked line of code.