org.mockito.exceptions.misusing.CannotStubVoidMethodWithReturnValue: 'close' is a *void method* and it *cannot* be stubbed with a *return value*! Voids are usually stubbed with Throwables: doThrow(exception).when(mock).someVoidMethod(); If you need to set the void method to do nothing you can use: doNothing().when(mock).someVoidMethod(); For more information, check out the javadocs for Mockito.doNothing(). *** If you're unsure why you're getting above error read on. Due to the nature of the syntax above problem might occur because: 1. The method you are trying to stub is *overloaded*. Make sure you are calling the right overloaded version. 2. Somewhere in your test you are stubbing *final methods*. Sorry, Mockito does not verify/stub final methods. 3. A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies - - with doReturn|Throw() family of methods. More in javadocs for Mockito.spy() method. 4. Mocking methods declared on non-public parent classes is not supported.