How to mock HTTPSession/FlexSession with TestNG and some Mocking Framework

Question

I'm developing a web application running on Tomcat 6, with Flex as Frontend. I'm testing my backend with TestNG. Currently, I'm trying to test the following method in my Java-Backend:

public class UserDAO extends AbstractDAO {
    (...)
    public UserPE login(String mail, String password) {
        UserPE dbuser = findUserByMail(mail); 
        if (dbuser == null || !dbuser.getPassword().equals(password))
            throw new RuntimeException("Invalid username and/or password");
        // Save logged in user
        FlexSession session = FlexContext.getFlexSession();
        session.setAttribute("user", dbuser);
        return dbuser;
    }
}    

The method needs access to the FlexContext which only exists when i run it on the Servlet container (don't bother if you don't know Flex, it's more a Java-Mocking question in general). Otherwise i get a Nullpointer exception when calling session.setAttribute(). Unfortunately, I cannot set the FlexContext from outside, which would make me able to set it from my tests. It's just obtained inside the method.

What would be the best way to test this method with a Mocking framework, without changing the method or the class which includes the method? And which framework would be the easiest for this use case (there are hardly other things i have to mock in my app, it's pretty simple)?

Sorry I could try out all of them for myself and see how i could get this to work, but i hope that i'll get a quickstart with some good advices!

Answer 1

Thanks to Derek Clarkson, I successfully mocked the FlexContext, making the login testable. Unfortunately, it's only possible with JUnit, as far as i see (tested all versions of TestNG with no success - the JMockit javaagent does not like TestNG, See this and this issues).

So this is how i'm doing it now:

public class MockTests {
    @MockClass(realClass = FlexContext.class)
    public static class MockFlexContext {
        @Mock
        public FlexSession getFlexSession() {
            System.out.println("I'm a Mock FlexContext.");
            return new FlexSession() {

                @Override
                public boolean isPushSupported() {
                    return false;
                }

                @Override
                public String getId() {
                    return null;
                }
            };
        }
    }

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
        Mockit.setUpMocks(MockFlexContext.class);
        // Test user is registered here
        (...)
    }

    @Test
    public void testLoginUser() {
        UserDAO userDAO = new UserDAO();
        assertEquals(userDAO.getUserList().size(), 1);
        // no NPE here 
        userDAO.login("asdf@asdf.de", "asdfasdf");
    }
}

For further testing i now have to implement things like the session map myself. But thats okay as my app and my test cases are pretty simple.