How to use inherit_public_method_from_interface method of org.mockito.internal.creation.InterfaceOverrideTest class

If the contract of class A includes the fact that it calls method B of an object of type C, then you should test this by making a mock of type C, and verifying that method B has been called.

This implies that the contract of class A has sufficient detail that it talks about type C (which might be an interface or a class). So yes, we're talking about a level of specification that goes beyond just "system requirements", and goes some way to describing implementation.

This is normal for unit tests. When you are unit testing, you want to ensure that each unit is doing the "right thing", and that will usually include its interactions with other units. "Units" here might mean classes, or larger subsets of your application.

Update:

I feel that this doesn't apply just to verification, but to stubbing as well. As soon as you stub a method of a collaborator class, your unit test has become, in some sense, dependent on implementation. It's kind of in the nature of unit tests to be so. Since Mockito is as much about stubbing as it is about verification, the fact that you're using Mockito at all implies that you're going to run across this kind of dependency.

In my experience, if I change the implementation of a class, I often have to change the implementation of its unit tests to match. Typically, though, I won't have to change the inventory of what unit tests there are for the class; unless of course, the reason for the change was the existence of a condition that I failed to test earlier.

So this is what unit tests are about. A test that doesn't suffer from this kind of dependency on the way collaborator classes are used is really a sub-system test or an integration test. Of course, these are frequently written with JUnit too, and frequently involve the use of mocking. In my opinion, "JUnit" is a terrible name, for a product that lets us produce all different types of test.

If you happen to be using Spring then it has a MockHttpServletResponse class.

@Test
public void myTest() {
    MockHttpServletResponse response = new MockHttpServletResponse();
    // Do test stuff here
    // Verify what was written to the response using MockHttpServletResponse's methods
    response.getContentAsString();
    response.getContentAsByteArray();
    response.getContentLength();
}

InOrder helps you to do that.

ServiceClassA firstMock = mock(ServiceClassA.class);
ServiceClassB secondMock = mock(ServiceClassB.class);

Mockito.doNothing().when(firstMock).methodOne();   
Mockito.doNothing().when(secondMock).methodTwo();  

//create inOrder object passing any mocks that need to be verified in order
InOrder inOrder = inOrder(firstMock, secondMock);

//following will make sure that firstMock was called before secondMock
inOrder.verify(firstMock).methodOne();
inOrder.verify(secondMock).methodTwo();

Make sure the hamcrest jar is higher on the import order than your JUnit jar.

JUnit comes with its own org.hamcrest.Matcher class that is probably being used instead.

You can also download and use the junit-dep-4.10.jar instead which is JUnit without the hamcrest classes.

mockito also has the hamcrest classes in it as well, so you may need to move\reorder it as well

You can use Mockitos Answer.

doAnswer(new Answer() {
     @Override
     public Object answer(InvocationOnMock invocation) {
         Object[] args = invocation.getArguments();
         ByteArrayOutputStream baos = (ByteArrayOutputStream)args[0];
         //fill baos with data
         return null;
     }
 }).when(client).retrieveFile(baos);

However, if you have possibility to refactor the tested code, better is to make client return the OutputStream or some data that can be put to this Output stream. This is would be much better design.

I changed the version of jupiter and junit to 5.3.2 and the problem has gone

The first issue is that you have to use spyTemp object to expect something from Mockito. Here it is not the same as test. spyTemp is wrapped by the Mockito object temp.

Another issue is that you stub only methodB(), but you are trying to run methodA(). Yes in your implementation of methodA() you call methodB(), but you call this.methodB(), not spyTemp.methodB(). Here you have to understand that mocking would work only when you call it on the instance of temp. It's wrapped by a Mockito proxy which catches your call, and if you have overriden some method, it will call your new implementation instead of the original one. But since the original method is called, inside it you know nothing about Mockito proxy. So your "overriden" method would be called only when you run spyTemp.methodB()

This should work:

Mockito.doReturn(true).when(spyTemp).methodB(Mockito.any()); 
boolean status = spyTemp.methodA("XYZ");

One way could be to avoid being too restrictive on your arguments in order to provide all the expected results with only one thenReturn call.

For example let's say that I want to mock this method:

public String foo(String firstArgument, Object obj) {
    return "Something";
}

You could then mock it by providing as many results as you want like below:

// Mock the call of foo of any String to provide 3 results
when(mock.foo(anyString(), anyObject())).thenReturn("val1", "val2", "val3");

Calls to foo with any parameters will provide respectively "val1", "val2", then any subsequent calls will provide "val3".

In case you do care about passed values but don't want to depend on call sequence you can use thenAnswer to provide an answer that matches with the second argument like you currently do but with 3 different thenReturn. Assuming that you have overridden the method equals(Object o).

when(mock.foo(anyString(), anyObject())).thenAnswer(
    invocation -> {
        Object argument = invocation.getArguments()[1];
        if (argument.equals(new ARequest(1, "A"))) {
            return new AResponse(1, "passed");
        } else if (argument.equals(new ARequest(2, "2A"))) {
            return new AResponse(2, "passed");
        } else if (argument.equals(new BRequest(1, "B"))) {
            return new BResponse(112, "passed");
        }
        throw new InvalidUseOfMatchersException(
            String.format("Argument %s does not match", argument)
        );
    }
);

Or simply, using the methods anyString and eq as argument marchers. Assuming that you have overridden the method equals(Object o).

when(service.foo(anyString(), eq(new ARequest(1, "A"))))
    .thenReturn(new AResponse(1, "passed"));
when(service.foo(anyString(), eq(new ARequest(2, "2A"))))
    .thenReturn(new AResponse(2, "passed"));
when(service.foo(anyString(), eq(new BRequest(1, "B"))))
    .thenReturn(new BResponse(112, "passed"));

You setup your mock to return something when it receives a given device objet:

        Device device = new Device() ;
        Mockito.when(deviceDao.save(device)).thenReturn(deviceEntity);

This tells your deviceDao mock to return deviceEntity when it receives device as a parameter to the save method.

Mockito uses equals for argument matching. This means that if you call deviceDao.save(x), deviceEntity will be returned if x.equals(device) is true.

Your method:

public String  show(){
        Device device = new Device() ;
        device.setContactName("abc");
        Device deviceEntity = deviceDao.save(device);
        System.out.println(deviceEntity);  // i get this null always Why ???
        return "demo";
}

This calls save() on a new Device instance. I highly doubt that this device is equal to the one you setup your mock with.

One way to solve this is to use a broader matcher in your test:

Mockito.when(deviceDao.save(any(Device.class)).thenReturn(deviceEntity);

Or simply to ensure that the Device that you setup your mock with is the same as the one used in your code. I can't provide you with an example since your question does not include the code for Device.equals().