How do you create unit tests for layered applications?

[paul.barry]

I am trying to figure out the best way to create unit tests for a web application that is separated into Presentation, Business and Persistence layers. I am working on a simple example of a user logging in with a username and password. So first I create a JavaBean to model a User:

package test.model;

public class User {

    private String username;
    private String password;
	
    //Getters/Setters...    
}

Next I create the business layer interface:

package test.service;

import test.model.User;

public interface UserService {

	public User login(String username, String password);
	
}

Then an implementation for the business layer:

package test.service.impl;

import test.dao.UserDAO;
import test.model.User;
import test.service.UserService;
import test.service.ex.ServiceException;
import test.util.StringUtil;


public class UserServiceImpl implements UserService {

    private UserDAO userDao;
    
    public User login(String username, String password) {
        User user = userDao.getByUsername(username);
        if(user == null) {
            throw new ServiceException("No user with username '"+username+"'");
        } else if(user.getPassword() == null || 
                !user.getPassword().equals(StringUtil.toMD5(password))) {
            throw new ServiceException("Password does not match");
        }
        
        return user;
    }

    //Getters/Setters...
}

So the business layer implementation depends on the persistence layer, so next I create the persistence layer interface:

package test.dao;

import test.model.User;

public interface UserDAO {

    public User getByUsername(String username);
    
}

And then I create a mock implementation:

package test.dao.mock;

import test.dao.UserDAO;
import test.model.User;

public class MockUserDAOImpl implements UserDAO {

    private User user = new User();
    
    public MockUserDAOImpl() {
        
        user.setUsername("user");
        //MD5 hash of "test"
        user.setPassword("098f6bcd4621d373cade4e832627b4f6");
        
    }
    
    public User getByUsername(String username) {
        if(user.getUsername().equalsIgnoreCase(username)) {
            return user;
        } else {
            return null;    
        }
    }

}

Eventually I would have a real DAO implementation with hibernate or something. Now I create the test for the service layer:

package test.service;

import test.model.User;
import test.service.ex.ServiceException;

public class UserServiceTest extends BaseServiceTestCase {

	private UserService service;
	
    public UserServiceTest() {
        super();
        service = (UserService)context.getBean("userService");
    }
    
    public void testLogin() throws Exception {
        User user = service.login("user","test");
        assertEquals("user",user.getUsername());
    }
    
    public void testLoginInvalidUsername() throws Exception {
        try {
            User user = service.login("wrong","test");
            fail("Service Exception should have been thrown");
        } catch(ServiceException ex) {}
    }
	
    public void testLoginIncorrectPassword() throws Exception {
        try {
            User user = service.login("user","wrong");
            fail("Service Exception should have been thrown");
        } catch(ServiceException ex) {}
    }	
    
    public void testLoginUsernameCaseSensitive() throws Exception {
        User user = service.login("uSeR","test");
        assertEquals("user",user.getUsername());
    }
    
    public void testLoginPasswordCaseSensitive() throws Exception {
        try {
            User user = service.login("user","tEsT");
            fail("Service Exception should have been thrown");
        } catch(ServiceException ex) {}
    }
    
}

BaseServiceTestCase takes care of looking up the context so that the userDao property of userService is set with an instance of MockUserDAOImpl. So now I have tests for my business layer.

So my question is where do I go from here? I will need to create a controller in the presentation layer. How do I create a unit test for that? It will obviously depend on an implementation of UserService. So do I just use the same userService with the Mock userDao in the controller? Doesn't that make the test not really a unit test? Do I have to create a MockUserServiceImpl that doesn't depend on a dao? Creating and maintaining all these mock implementations is a lot of overhead, isn't it?

[katentim]

Consider using EasyMock and/or JMock to make your tests more modular.

For controller testing, you might find this thread useful.

Also, take a look at the petclinic sample and Spring test source tree (both in the distribution).

[paul.barry]

I did take a look at the petclinic sample, but that only has integration tests for the DAO layer. I don't see any tests for the conroller. Plus the petstore doesn't really have a business layer, just one DAO (Clinic) that is called by the controller.

I think you are right, dynamic mocks seem to be the way to go. I just read the chapter in Spring Live about using Dynamic Mocks, very helpful. It seems like what Matt Raible is saying is that you shold create 4 types of tests:

Integration Tests for the DAO layer
Unit Tests for the Business (Service/Manager/etc.) layer, with Mock DAOs
Unit Tests for the Controllers, with Mock Services/Managers
Integration Tests for the Views with jWebUnit or Canoo