[FIXED] How do I test business logic in a servlet using Junit?

Issue

I'm having a servlet that does some pre-condition checks before invoking a DAO method, like following:

private void processRequest(HttpServletRequest request, HttpServletResponse response){
        if(a condition is met)
            myDAOFunction();
        else
            redirect();
}

How should I construct my unit test to verify whether with a certain request, the servlet invokes my function, and with other requests that does not meet the condition then it will redirect the page?

I have tried this solution: Since my DAO function would make some changes in the database if it were called, and through that I can test if the servlet handles the requests and responses correctly. But I figure that is not quite an elegant solution.

Solution

So what you need to verify if the servlet can interact with the DAO related codes correctly. If your design already separate and encapsulate all the codes related to interacting with DB in a DAO service class , you can easily test it by mocking this DAO service class using Mockito and then verify if the expected methods on the mock DAO service are invoked with the expected parameters. If not , please refractor your codes such that it will have this separate DAO service class.

For mocking MockHttpServletRequest and MockHttpServletResponse , spring-test already provides some utilities to create them which are useful for testing the Servlet stuff. Although they are primarily designed to work with the codes written by spring-mvc , it should also be used for the codes that are not written by spring and should be more convenient to use when compared Mockito.

Assuming your servlet is called FooBarServlet, the test case may look like :

@ExtendWith(MockitoExtension.class)
public class FooBarServletTest { 

        @Mock
        DaoService daoService;

        @Test
        void testSaveToDatabase(){
                    
            FooBarServlet sut = new FooBarServlet(daoService);

            MockHttpServletRequest request = MockMvcRequestBuilders.get("/foobar")
                ......   
                .buildRequest(new MockServletContext());
            MockHttpServletResponse response = new MockHttpServletResponse();

            sut.processRequest(request, response);
            verify(daoService).save("xxxxxx");

        }

        @Test
        void testRedirect(){
                    
            FooBarServlet sut = new FooBarServlet(daoService);

            MockHttpServletRequest request = MockMvcRequestBuilders.get("/foobar")
                ......   
                .buildRequest(new MockServletContext());
            MockHttpServletResponse response = new MockHttpServletResponse();

            sut.processRequest(request, response);
            verify(daoService,never()).save(any());
        }

}

Answered By - Ken Chan
Answer Checked By - Marie Seifert (JavaFixing Admin)