jUnit - How to assert that inherited methods are invoked?

Question

Let's say you have some 3rd-party library class that you want to extend, simply to add convenience methods to it (so you can call an inherited method with default parameters for example).

Using jUnit/jMock, is it possible to write an assertion / mock expection that tests that the correct inherited method is called?

For example, something like this:

class SomeClass extends SomeLibraryClass {
    public String method(String code) {
         return method(code, null, Locale.default());
    }
}

How can I assert that method is being called?

Answer 1

You can make a further subclass inside your unit test that actually tells you:

public class MyTest {
    boolean methodCalled = false;

    @Test
    public void testMySubclass(){
          TestSomeClass testSomeClass = new TestSomeClass();
          .. invoke method on testSomeclass ..
          aseertTrue( methodCalled);

    }  
    class TestSomeClass extends SomeClass{
        public String method(String code){
              methodCalled = true;
        } 
     }
}

Answer 2

Unit testing is more useful to verify the functionality of given methods, not to assert coverage. Unit tests that care more about what method got called know way more about the classes they are testing than they probably should, not to mention will be confusing to the reader.

Coverage tools like Cobertura or EMMA will tell you whether you properly covered your code.

Answer 3

it's hard to tell without a more concrete example, but I'd guess that this ought to be an integration test--test the whole package together--rather than a unit test. Sometimes one can be too fine-grained with unit testing.

Answer 4

It may indeed be better to only write integration tests in this case, but if you really want a unit test, you can have it just as easily as in any other case:

public class SomeClassTest
{
    @Test
    public void testMethod()
    {
        final String code = "test";

        new Expectations()
        {
            SomeLibraryClass mock;

            {
                mock.method(code, null, (Locale) any);
            }
        };

        new SomeClass().method(code);
    }
}

This test uses the JMockit mocking API.