Как тестить сервлеты в юнит тестах

Для этого нам понадобятся следующие библиотеки:
- org.springframework:spring-test:4.1.7.RELEASE (для моков запроса и ответа)
- org.jsoup:jsoup:1.7.3 (для разбора хтмл страницы и выборки элементов на ней)
- шаблонизатор для генерации хтмл ответа сервлеты(ну можно например воспользоваться com.github.spullara.mustache.java:compiler:0.9.0)



Создаем базовый класс для всех наших тестов для сервлет:

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.net.URI;
import java.util.Map;

public abstract class BaseServletTest {
    protected Document page;
    protected MockHttpServletResponse lastResponse;
    private HttpServlet servlet;

    public HttpServlet getServlet() {
        if (servlet != null) return servlet;
        return servlet = createServlet();
    }

    protected abstract HttpServlet createServlet();

    protected void get(String pathAndQuery) throws ServletException, IOException {
        MockHttpServletRequest request = createRequest(pathAndQuery);
        request.setMethod("GET");
        doRequest(request);
    }

    protected void post(String pathAndQuery, Map params) throws ServletException, IOException {
        MockHttpServletRequest request = createRequest(pathAndQuery);
        request.addParameters(params);
        request.setMethod("POST");
        doRequest(request);
    }

    private void doRequest(HttpServletRequest request) throws ServletException, IOException {
        MockHttpServletResponse response = new MockHttpServletResponse();
        getServlet().service(request, response);
        page = Jsoup.parse(response.getContentAsString());
        lastResponse = response;
    }

    private MockHttpServletRequest createRequest(String pathAndQuery) {
        URI uri = getUri(pathAndQuery);
        MockHttpServletRequest request = new MockHttpServletRequest();
        request.setRequestURI(uri.getPath());
        request.setQueryString(uri.getQuery());
        return request;
    }

    private URI getUri(String pathAndQuery) {
        return URI.create("http://example.org" + pathAndQuery);
    }
}

А теперь вот созданим на его основе юнит тест:

import org.junit.Test;
import shouty.core.Person;

import javax.servlet.ServletException;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import static java.util.Arrays.asList;
import static org.hamcrest.CoreMatchers.containsString;
import static org.junit.Assert.*;
import static org.mockito.Mockito.*;

public class ShoutyServletTest extends BaseServletTest {
    private final HashMap users = new HashMap(){{
        put("root", mock(Root.class));
        put("publisher", mock(Publisher.class));
    }};

    @Test
    public void getShouldRespondWithHomepageForKnownUser() throws Exception {
        get("/?param=value");
        assertEquals(200, lastResponse.getStatus());
    }

    @Test
    public void getShouldRespondWith401WhenUserNotRecognised() throws Exception {
        get("/private/path");
        assertEquals(401, lastResponse.getStatus());
        assertThat(lastResponse.getErrorMessage(), containsString("Unauthorized"));
    }

    @Test
    public void getRendersForTheHomepage() throws Exception {
        get("/");
        assertNotNull(page.select("h1#homeH1"));
    }

    @Test
    public void getDisplaysMessagesHeardByUser() throws ServletException, IOException {
        List messages = asList("one", "two");
        Person lucy = mock(Person.class);
        when(lucy.getMessagesHeard()).thenReturn(messages);
        people.put("Lucy", lucy);
        get("/?name=Lucy");
        assertEquals("one", page.select(".message").get(0).text());
        assertEquals("two", page.select(".message").get(1).text());
    }

    @Override
    protected MyServlet createServlet() {
        return new MyServlet(people);
    }
}

Пример сервлеты:

import com.github.mustachejava.DefaultMustacheFactory;
import com.github.mustachejava.Mustache;
import com.github.mustachejava.MustacheFactory;
import User;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;

public class MyServlet extends HttpServlet {
    private final MustacheFactory mf = new DefaultMustacheFactory();
    private final Mustache indexTemplate = mf.compile("templates/index.mustache");
    private Map users;

    public ShoutyServlet(Map users) {
        this.users = users;
    }

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        if (!authenticated(req)) {
            sendAuthenticationError(req, res);
            return;
        }

        Map context = new HashMap<>();
        context.put("name", getName(req));
        context.put("greetings", getUser(req).getGreetings());
        indexTemplate.execute(res.getWriter(), context).flush();
    }

    private User getUser(HttpServletRequest req) throws UnsupportedEncodingException {
        return users.get(getName(req));
    }

    private void sendAuthenticationError(HttpServletRequest req, HttpServletResponse res) throws IOException {
        res.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Unauthorized: " + getName(req));
    }

    private boolean authenticated(HttpServletRequest req) throws IOException {
        return users.containsKey(getName(req));
    }

    private String getName(HttpServletRequest req) throws UnsupportedEncodingException {
        Map queryParams = QueryString.toMap(req.getQueryString());
        return queryParams.get("name");
    }
}

Пример шаблона:

<!DOCTYPE html>
<html>
<body>
<h1 class="homeH1">{{personName}}"</h1>
<ul>
    {{#greetings}}
    <li class="greeting">{{.}}</li>
    {{/greetings}}
</ul>
</body>
</html>