The following code shows a typical JMock2 mock object usage pattern. In this example, we test the Product class and we use a mock ProductType object to test Product's interaction with ProductType.

@Before
public void setUp() {
    context = new JUnit4Mockery();
}

@test
public void testProductInteractionWithProductType(){
    Product productImpl = new ProductImpl();
    
    //Create a mock object to mock a product type
    final ProductType mockProductType = context.mock(ProductType.class);
    
    //Pass the mock object to the product class
    productImpl.setProductType(mockProductType);
    
    //Create the object that the mock object returns
    AttributeGroup expectedAttributeGroup = new AttributeGroupImpl();
    
    //Specify that the product type's getProductAttributeGroup() method must
    //be called one time and that it will return to the product the attribute
    //group we wish to test the product with
    context.checking(new Expectations() {
            {
                oneOf(mockProductType).getProductAttributeGroup();
                will(returnValue(expectedAttributeGroup));
            }
        });
        
    //Invoke the method being tested, which will interact with the mock object
    AttributeGroup returnedAttributeGroup = productImpl.getAttributeGroup();
    
    //Check the results of the operation here
    assertAttributeGroupsAreEqual(expectedAttributeGroup, returnedAttributeGroup);
}

Jmock is very strict regarding types in constraints. For example, take the get() method siganature in the PersistencEngine class shown below:

Persistence get(final Class persistenceClass, final long uidPk) throws EpPersistenceException;

This method cannot be mocked as shown below because the "1" that is passed to equals is an int instead of a long.

allowing(mockPersistenceEngine).get(with(equal(Brand.class)), with(equal(1)));
will(returnValue(brand1));

Instead, the method must be mocked with the type explicitly stated as shown below.

allowing(mockPersistenceEngine).get(with(equal(Brand.class)), with(equal(1L)));
will(returnValue(brand1));