Question

I’m wondering how to go about checking that a method returns a container encapsulating some collection which is the aggregate of multiple other containers returned by mock objects. That is, it contains all the elements of the individual containers. I have some tests elsewhere that check the container ‘works’ (add/addAll/etc), so I know that works, but I’m not sure how go about with the test below ‘createsRoadUsersAccordingToAllAddedCreators’.

I have a RoadUserCreationDaemon class which I call create upon which returns a RoadUserContainer according to added RoadUserCreator’s. A simplified version:

public class RoadUserCreationDaemon {

    private SimulationManager simulationManager;
    private List<RoadUserCreator> roadUserCreators;

    public RoadUserCreationDaemon(SimulationManager simulationManager) {
        this.simulationManager = simulationManager;
        roadUserCreators = new ArrayList<RoadUserCreator>();
    }

    public void addRoadUserCreator(RoadUserCreator roadUserCreator) {
        roadUserCreators.add(roadUserCreator);
    }

    public RoadUserContainer createRoadUsers() {
        RoadUserContainer roadUsers = new RoadUserContainerImpl(); 
        for (RoadUserCreator creator : roadUserCreators) {
            roadUsers.addAll(createRoadUsers(creator));
        }
        return roadUsers;
    }

    public RoadUserContainer createRoadUsers(
            RoadUserCreator roadUserCreator) {
        return roadUserCreator.create();
    }
}

I started by writing a test (JUnit4 / JMock2.5.1) for createRoadUsers which returns a RoadUserContainer with a supplied creator. Then I started writing a test for a non-parameterised createRoadUsers to see if it returns a container with all the elements of the individual containers returned by the creators:

@RunWith(JMock.class)
public class TestRoadUserCreationDaemon {
    Mockery context = new JUnit4Mockery();      
    private RoadUserCreationDaemon daemon;      
    private RoadUserCreator roadUserCreator;    
    private SimulationManager simulationManager;        
    private RoadUserContainer createdRoadUsers;

    @Before
    public void setUp() {
        simulationManager = context.mock(SimulationManager.class);
        daemon = new RoadUserCreationDaemon(simulationManager);

        roadUserCreator = context.mock(RoadUserCreator.class);
        createdRoadUsers = context.mock(RoadUserContainer.class);
    }       

    @Test
    public void createsRoadUsersAccordingToAllAddedCreators() throws Exception {
        final RoadUserCreator anotherRoadUserCreator = context.mock(RoadUserCreator.class, "anotherRUC");
        final RoadUserContainer moreCreatedRoadUsers = context.mock(RoadUserContainer.class, "moreCRU");
        context.checking(new Expectations() {{
            oneOf (roadUserCreator).create(); will(returnValue(createdRoadUsers));
            oneOf (anotherRoadUserCreator).create(); will(returnValue(moreCreatedRoadUsers));

            oneOf (createdRoadUsers).roadUsersAsList();
            oneOf (moreCreatedRoadUsers).roadUsersAsList();
        }});

        daemon.addRoadUserCreator(roadUserCreator);
        daemon.addRoadUserCreator(anotherRoadUserCreator);
        daemon.createRoadUsers();

        //how to easily check that the two lists are equivilant - have same items, but not the same object?
        //assertEquals(createdRoadUsers, daemon.createRoadUsers() );
    }

    @Test
    public void createsRoadUsersAccordingToCreator() throws Exception {

        context.checking(new Expectations() {{
            oneOf (roadUserCreator).create(); will(returnValue(createdRoadUsers));
        }});
        assertEquals(createdRoadUsers, daemon.createRoadUsers(roadUserCreator));
    }
}

As the comment says…I’m not sure how to proceed in a non-ugly way.

The ‘RoadUserContainer’ interface:

public interface RoadUserContainer extends Iterable<RoadUser> {
    public void add(RoadUser roadUser);
    public Iterator<RoadUser> iterator();
    public void addAll(RoadUserContainer createRoadUsers);
    public List<RoadUser> roadUsersAsList();
    public boolean equals(RoadUserContainer otherContainer);
    ...
}

I am new to TDD and mocking, and this is my first Java project for >6 years, so feel free to comment on ancillary aesthetics!

Answer 1

I would probably initially use real containers and mock the other objects. Then use hamcrest to interrogate the resulting object.

The test I would want to create would look something like this:

final RoadUser roadUser0 = context.mock(RoadUser.class, "roadUser0");
final RoadUser roadUser1 = context.mock(RoadUser.class, "roadUser1");
final RoadUser roadUser2 = context.mock(RoadUser.class, "roadUser2");

final RoadUserCreator roadUserCreator0 = context.mock(RoadUserCreator.class, "roadUserCreator0");
final RoadUserCreator roadUserCreator1 = context.mock(RoadUserCreator.class, "roadUserCreator1");

final RoadUserCreationDaemon daemon = new RoadUserCreationDaemon(null);
daemon.addRoadUserCreator(roadUserCreator0);
daemon.addRoadUserCreator(roadUserCreator1);        

context.checking(new Expectations() {{
    oneOf(roadUserCreator0).create(); will(returnValue(roadUsers(roadUser0, roadUser1)));
    oneOf(roadUserCreator1).create(); will(returnValue(roadUsers(roadUser2)));
}});

assertThat(daemon.createRoadUsers(), contains(roadUser0, roadUser1, roadUser2));

you will need these imports from hamcrest:

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.contains;

If order is not important you could use containsInAnyOrder instead of contains

you would also need to create the utility method “roadUsers”

public static RoadUserContainer roadUsers(final RoadUser... roadUsers)
{
    return new RoadUserContainerImpl(roadUsers);
}

---

An alternative design would be to change the interface of the RoadUserCreationDaemon

public void createRoadUsers(final RoadUserContainer roadUsers) {
    for (final RoadUserCreator roadUserCreator : roadUserCreators) {
        roadUsers.addAll(roadUserCreator.create());
    }
}

Then you could write the tests like this:

final RoadUserContainer roadUserContainer0 = context.mock(RoadUserContainer.class, "roadUserContainer0");
final RoadUserContainer roadUserContainer1 = context.mock(RoadUserContainer.class, "roadUserContainer1");

final RoadUserContainer resultRoadUserContainer = context.mock(RoadUserContainer.class, "resultRoadUserContainer");

final RoadUserCreator roadUserCreator0 = context.mock(RoadUserCreator.class, "roadUserCreator0");
final RoadUserCreator roadUserCreator1 = context.mock(RoadUserCreator.class, "roadUserCreator1");

final RoadUserCreationDaemon daemon = new RoadUserCreationDaemon(null);
daemon.addRoadUserCreator(roadUserCreator0);
daemon.addRoadUserCreator(roadUserCreator1);

context.checking(new Expectations() {
    {
        oneOf(roadUserCreator0).create();
        will(returnValue(roadUserContainer0));
        oneOf(roadUserCreator1).create();
        will(returnValue(roadUserContainer1));

        oneOf(resultRoadUserContainer).addAll(roadUserContainer0);
        oneOf(resultRoadUserContainer).addAll(roadUserContainer1);
    }
});

daemon.createRoadUsers(resultRoadUserContainer);

If the order of the calls to “addAll” is important you can use a jmock sequence