Unit testing a Java Servlet

Question

I would like to know what would be the best way to do unit testing of a servlet.

Testing internal methods is not a problem as long as they don\'t refer to the servl

Answer 1

This implementation of a JUnit test for servlet doPost() method relies only on the Mockito library for mocking up instances of HttpRequest, HttpResponse, HttpSession, ServletResponse and RequestDispatcher. Replace parameter keys and JavaBean instance with those that correspond to values referenced in the associated JSP file from which doPost() is called.

Mockito Maven dependency:

      org.mockito
      mockito-all
      1.9.5

JUnit test:

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import java.io.IOException;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import static org.mockito.Mockito.*;

/**
 * Unit tests for the {@code StockSearchServlet} class.
 * @author Bob Basmaji
 */
public class StockSearchServletTest extends HttpServlet {
    // private fields of this class
    private static HttpServletRequest request;
    private static HttpServletResponse response;
    private static StockSearchServlet servlet;
    private static final String SYMBOL_PARAMETER_KEY = "symbol";
    private static final String STARTRANGE_PARAMETER_KEY = "startRange";
    private static final String ENDRANGE_PARAMETER_KEY = "endRange";
    private static final String INTERVAL_PARAMETER_KEY = "interval";
    private static final String SERVICETYPE_PARAMETER_KEY = "serviceType";

    /**
     * Sets up the logic common to each test in this class
     */
    @Before
    public final void setUp() {
        request = mock(HttpServletRequest.class);
        response = mock(HttpServletResponse.class);

        when(request.getParameter("symbol"))
                .thenReturn("AAPL");

        when(request.getParameter("startRange"))
                .thenReturn("2016-04-23 00:00:00");

        when(request.getParameter("endRange"))
                .thenReturn("2016-07-23 00:00:00");

        when(request.getParameter("interval"))
                .thenReturn("DAY");

        when(request.getParameter("serviceType"))
                .thenReturn("WEB");

        String symbol = request.getParameter(SYMBOL_PARAMETER_KEY);
        String startRange = request.getParameter(STARTRANGE_PARAMETER_KEY);
        String endRange = request.getParameter(ENDRANGE_PARAMETER_KEY);
        String interval = request.getParameter(INTERVAL_PARAMETER_KEY);
        String serviceType = request.getParameter(SERVICETYPE_PARAMETER_KEY);

        HttpSession session = mock(HttpSession.class);
        when(request.getSession()).thenReturn(session);
        final ServletContext servletContext = mock(ServletContext.class);
        RequestDispatcher dispatcher = mock(RequestDispatcher.class);
        when(servletContext.getRequestDispatcher("/stocksearchResults.jsp")).thenReturn(dispatcher);
        servlet = new StockSearchServlet() {
            public ServletContext getServletContext() {
                return servletContext; // return the mock
            }
        };

        StockSearchBean search = new StockSearchBean(symbol, startRange, endRange, interval);
        try {
            switch (serviceType) {
                case ("BASIC"):
                    search.processData(ServiceType.BASIC);
                    break;
                case ("DATABASE"):
                    search.processData(ServiceType.DATABASE);
                    break;
                case ("WEB"):
                    search.processData(ServiceType.WEB);
                    break;
                default:
                    search.processData(ServiceType.WEB);
            }
        } catch (StockServiceException e) {
            throw new RuntimeException(e.getMessage());
        }
        session.setAttribute("search", search);
    }

    /**
     * Verifies that the doPost method throws an exception when passed null arguments
     * @throws ServletException
     * @throws IOException
     */
    @Test(expected = NullPointerException.class)
    public final void testDoPostPositive() throws ServletException, IOException {
        servlet.doPost(null, null);
    }

    /**
     * Verifies that the doPost method runs without exception
     * @throws ServletException
     * @throws IOException
     */
    @Test
    public final void testDoPostNegative() throws ServletException, IOException {
        boolean throwsException = false;
        try {
            servlet.doPost(request, response);
        } catch (Exception e) {
            throwsException = true;
        }
        assertFalse("doPost throws an exception", throwsException);
    }
}