How to use should_mock_method_of_package_private_class method of org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMakerTest class

It sounds like you may want to be using the .expects(1) type methods that mock frameworks usually provide.

Using mockito, if you were testing a List and wanted to verify that clear was called 3 times and add was called at least once with these parameters you do the following:

List mock = mock(List.class);        
someCodeThatInteractsWithMock();                 

verify(mock, times(3)).clear();
verify(mock, atLeastOnce()).add(anyObject());      

Source - MockitoVsEasyMock

I think you do need to cast it, but it shouldn't be too bad:

Foo<Bar> mockFoo = (Foo<Bar>) mock(Foo.class);
when(mockFoo.getValue()).thenReturn(new Bar());

I got this when combining PowerMock with Mockito. Fixed by using compatible version as shown here: https://github.com/powermock/powermock/wiki/Mockito#supported-versions

I would try any(byte[].class)

Mockito 1.10.5 has introduced this feature.

For the code sample in the question, here is one way to capture the varargs:

    ArgumentCaptor<String> varArgs = ArgumentCaptor.forClass(String.class);
    A mock = Mockito.mock(A.class);
    mock.setNames("Jeff", "Mike", "John");
    Mockito.verify(mock).setNames(varArgs.capture());

    //Results may be validated thus:
    List<String> expected = Arrays.asList("Jeff", "Mike", "John");
    assertEquals(expected, varArgs.getAllValues());

Please see the ArgumentCaptor javadoc for details.

Fail the test if an exception is caught.

@Test
public void testGetBalanceForPerson() {

   // creating mock person
   Person person1 = mock(Person.class);
   when(person1.getId()).thenReturn("mockedId");

   // calling method under test
   try {
      myClass.getBalanceForPerson(person1);
   } catch(Exception e) {
      fail("Should not have thrown any exception");
   }
}

Michael's answer is very close, but here is the example that works.

I already use Mockito for my unit tests, so I am familiar with the library. However, unlike my previous experience with Mockito, simply mocking the return result does not help. I need to do two things to test all of the use cases:

1. Modify the value stored in the StreamResult.
2. Throw a SoapFaultClientException.

First, I needed to realize that I cannot mock WebServiceTemplate with Mockito since it is a concrete class (you need to use EasyMock if this is essential). Luckily, the call to the web service, sendSourceAndReceiveToResult, is part of the WebServiceOperations interface. This required a change to my code to expect a WebServiceOperations vs a WebServiceTemplate.

The following code supports the first use case where a result is returned in the StreamResult parameter:

private WebServiceOperations getMockWebServiceOperations(final String resultXml)
{
  WebServiceOperations mockObj = Mockito.mock(WebServiceOperations.class);

  doAnswer(new Answer()
  {
    public Object answer(InvocationOnMock invocation)
    {
      try
      {
        Object[] args = invocation.getArguments();
        StreamResult result = (StreamResult)args[2];
        Writer output = result.getWriter();
        output.write(resultXml);
      }
      catch (IOException e)
      {
        e.printStackTrace();
      }

      return null;
    }
  }).when(mockObj).sendSourceAndReceiveToResult(anyString(), any(StreamSource.class), any(StreamResult.class));

  return mockObj;
}

The support for the second use case is similar, but requires the throwing of an exception. The following code creates a SoapFaultClientException which contains the faultString. The faultCode is used by the code I am testing which handles the web service request:

private WebServiceOperations getMockWebServiceOperations(final String faultString)
{
  WebServiceOperations mockObj = Mockito.mock(WebServiceOperations.class);

  SoapFault soapFault = Mockito.mock(SoapFault.class);
  when(soapFault.getFaultStringOrReason()).thenReturn(faultString);

  SoapBody soapBody = Mockito.mock(SoapBody.class);
  when(soapBody.getFault()).thenReturn(soapFault);

  SoapMessage soapMsg = Mockito.mock(SoapMessage.class);
  when(soapMsg.getSoapBody()).thenReturn(soapBody);

  doThrow(new SoapFaultClientException(soapMsg)).when(mockObj).sendSourceAndReceiveToResult(anyString(), any(StreamSource.class), any(StreamResult.class));

  return mockObj;
}

More code may be required for both of these use cases, but they work for my purposes.

You don't need MockRestServiceServer object. The annotation is @InjectMocks not @Inject. Below is an example code that should work

@RunWith(MockitoJUnitRunner.class)
public class SomeServiceTest {
    @Mock
    private RestTemplate restTemplate;

    @InjectMocks
    private SomeService underTest;

    @Test
    public void testGetObjectAList() {
        ObjectA myobjectA = new ObjectA();
        //define the entity you want the exchange to return
        ResponseEntity<List<ObjectA>> myEntity = new ResponseEntity<List<ObjectA>>(HttpStatus.ACCEPTED);
        Mockito.when(restTemplate.exchange(
            Matchers.eq("/objects/get-objectA"),
            Matchers.eq(HttpMethod.POST),
            Matchers.<HttpEntity<List<ObjectA>>>any(),
            Matchers.<ParameterizedTypeReference<List<ObjectA>>>any())
        ).thenReturn(myEntity);

        List<ObjectA> res = underTest.getListofObjectsA();
        Assert.assertEquals(myobjectA, res.get(0));
    }

There a Spring test annotation (org.springframework.security.test.context.support.WithMockUser) which does this for you...

@Test
@WithMockUser(username = "myUser", roles = { "myAuthority" })
public void aTest(){
    // any usage of `Authentication` in this test invocation will get an instance with the user name "myUser" and a granted authority "myAuthority"
    // ...
}

Alternatively, you can continue with your current approach by mocking Spring's Authentication. For example, in your test case:

Authentication authentication = Mockito.mock(Authentication.class);

Then tell Spring's SecurityContextHolder to store this Authentication instance:

SecurityContext securityContext = Mockito.mock(SecurityContext.class);
Mockito.when(securityContext.getAuthentication()).thenReturn(auth);
SecurityContextHolder.setContext(securityContext);

Now, if your code needs Authentication to return something (the user name perhaps) you just set some expectations on the mocked Authentication instance in the usual way e.g.

Mockito.when(authentication.getName()).thenReturn("aName");

This is quite close to what you are already doing but you have just mocked the wrong type.

Update 1: in response to this update to the OP:

I now can get rid of the error in the testing class. I debugged into the code, see that the securityContext has value when I am in the testing class. But when I jump to the code inside the controller advice, the below get returns null:

SecurityContextHolder.getContext().getAuthentication().getPrincipal()

You just need to set an expectation on the mocked Authentication, for example:

UsernamePasswordAuthenticationToken principal = new UsernamePasswordAuthenticationToken("aUserName", "aPassword");
Mockito.when(authentication.getPrincipal()).thenReturn(principal);

With the above code this line ...

SecurityContextHolder.getContext().getAuthentication().getPrincipal();

... will return that UsernamePasswordAuthenticationToken.

Since you use a custom type (ApiKeyAuthentication, I think?) you should just let authentication.getPrincipal() return that type instead of a UsernamePasswordAuthenticationToken.