一个Easy Mock案例（servelet）

一个Easy Mock案例（servelet）

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• 测试方法

Servlet 单元测试 软件测试 junit XP

单元测试是XP极力推荐的测试驱动 开发模式，是保证软件 质量的重要方法。尽管如此，对许多类的单元测试仍然是极其困难的，例如，对数据库操作的类进行测试，如果不准备好数据库环境以及相关测试数据，是很难进行单元测试的；再例如，对需要运行在容器内的Servlet或EJB组件，脱离了容器也难于测试。



幸运的是，Mock Object可以用来模拟一些我们需要的类，这些对象被称之为模仿对象，在单元测试中它们特别有价值。



Mock Object用于模仿真实对象的方法调用，从而使得测试不需要真正的依赖对象。Mock Object只为某个特定的测试用例的场景提供刚好满足需要的最少功能。它们还可以模拟错误的条件，例如抛出指定的异常等。



目前，有许多可用的Mock类库可供我们选择。一些Mock库提供了常见的模仿对象，例如：HttpServletRequest，而另一些Mock库则提供了动态生成模仿对象的功能，本文将讨论使用EasyMock动态生成模仿对象以便应用于单元测试。



到目前为止，EasyMock提供了1.2版本和2.0版本，2.0版本仅支持Java SE 5.0，本例中，我们选择EasyMock 1.2 for Java 1.3版本进行测试，可以从http://www.easymock.org/ 下载合适的版本。



我们首先来看一个用户验证的LoginServlet类：

 packagecom.jeffhanson.geronimo.jmx;

 importjava.io.*;

 importjavax.servlet.*;

 importjavax.servlet.http.*;

 publicclassLoginServletextendsHttpServlet{

 protectedvoiddoPost(HttpServletRequestrequest,
 HttpServletResponseresponse)throwsServletException,IOException{

 Stringusername=request.getParameter("username");

 Stringpassword=request.getParameter("password");

 //checkusername&password:

 if("admin".equals(username)&&"123456".equals(password)){

ServletContextcontext=getServletContext();

RequestDispatcherdispatcher=context
 .getNamedDispatcher("dispatcher");

dispatcher.forward(request,response);

}

 else{

 thrownewRuntimeException("Loginfailed.");

}

}

}

 packagecom.jeffhanson.geronimo.jmx;

 importjava.io.*;

 importjavax.servlet.*;

 importjavax.servlet.http.*;

 publicclassLoginServletextendsHttpServlet{

 protectedvoiddoPost(HttpServletRequestrequest,
 HttpServletResponseresponse)throwsServletException,IOException{

 Stringusername=request.getParameter("username");

 Stringpassword=request.getParameter("password");

 //checkusername&password:

 if("admin".equals(username)&&"123456".equals(password)){

ServletContextcontext=getServletContext();

RequestDispatcherdispatcher=context
 .getNamedDispatcher("dispatcher");

dispatcher.forward(request,response);

}

 else{

 thrownewRuntimeException("Loginfailed.");

}

}

}

package com.jeffhanson.geronimo.jmx; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class LoginServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); // check username & password: if ("admin".equals(username) && "123456".equals(password)) { ServletContext context = getServletContext(); RequestDispatcher dispatcher = context .getNamedDispatcher("dispatcher"); dispatcher.forward(request, response); } else { throw new RuntimeException("Login failed."); } } } package com.jeffhanson.geronimo.jmx; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class LoginServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); // check username & password: if ("admin".equals(username) && "123456".equals(password)) { ServletContext context = getServletContext(); RequestDispatcher dispatcher = context .getNamedDispatcher("dispatcher"); dispatcher.forward(request, response); } else { throw new RuntimeException("Login failed."); } } } 这个Servlet实现简单的用户验证的功能，若用户名和口令匹配“admin”和“123456”，则请求被转发到指定的dispatcher上，否则，直接抛出RuntimeException。



为了测试doPost()方法，我们需要模拟HttpServletRequest，ServletContext和RequestDispatcher对象，以便脱离J2EE容器来测试这个Servlet。



我们建立TestCase，名为LoginServletTest：

publicclassLoginServletTestextendsTestCase{

}

 publicclassLoginServletTestextendsTestCase{

}

public class LoginServletTest extends TestCase { } public class LoginServletTest extends TestCase { } 我们首先测试当用户名和口令验证失败的情形，演示如何使用EasyMock来模拟HttpServletRequest对象：

publicvoidtestLoginFailed()throwsException{

 MockControlmc=MockControl.createControl(HttpServletRequest.class);

HttpServletRequestrequest=(HttpServletRequest)mc.getMock();

 //setMockObjectbehavior:

 request.getParameter("username");

 mc.setReturnValue("admin",1);

 request.getParameter("password");

 mc.setReturnValue("1234",1);

 //ok,allbehaviorsareset!

mc.replay();

 //nowstarttest:

 LoginServletservlet=newLoginServlet();

 try{

 servlet.doPost(request,null);

 fail("Notcaughtexception!");

}

 catch(RuntimeExceptionre){

 assertEquals("Loginfailed.",re.getMessage());

}

 //verify:

mc.verify();

}

 publicvoidtestLoginFailed()throwsException{

 MockControlmc=MockControl.createControl(HttpServletRequest.class);

HttpServletRequestrequest=(HttpServletRequest)mc.getMock();

 //setMockObjectbehavior:

 request.getParameter("username");

 mc.setReturnValue("admin",1);

 request.getParameter("password");

 mc.setReturnValue("1234",1);

 //ok,allbehaviorsareset!

mc.replay();

 //nowstarttest:

 LoginServletservlet=newLoginServlet();

 try{

 servlet.doPost(request,null);

 fail("Notcaughtexception!");

}

 catch(RuntimeExceptionre){

 assertEquals("Loginfailed.",re.getMessage());

}

 //verify:

mc.verify();

}

public void testLoginFailed() throws Exception { MockControl mc = MockControl.createControl(HttpServletRequest.class); HttpServletRequest request = (HttpServletRequest) mc.getMock(); // set Mock Object behavior: request.getParameter("username"); mc.setReturnValue("admin", 1); request.getParameter("password"); mc.setReturnValue("1234", 1); // ok, all behaviors are set! mc.replay(); // now start test: LoginServlet servlet = new LoginServlet(); try { servlet.doPost(request, null); fail("Not caught exception!"); } catch (RuntimeException re) { assertEquals("Login failed.", re.getMessage()); } // verify: mc.verify(); } public void testLoginFailed() throws Exception { MockControl mc = MockControl.createControl(HttpServletRequest.class); HttpServletRequest request = (HttpServletRequest) mc.getMock(); // set Mock Object behavior: request.getParameter("username"); mc.setReturnValue("admin", 1); request.getParameter("password"); mc.setReturnValue("1234", 1); // ok, all behaviors are set! mc.replay(); // now start test: LoginServlet servlet = new LoginServlet(); try { servlet.doPost(request, null); fail("Not caught exception!"); } catch (RuntimeException re) { assertEquals("Login failed.", re.getMessage()); } // verify: mc.verify(); } 仔细观察测试代码，使用EasyMock来创建一个Mock对象需要首先创建一个MockControl：

MockControl mc = MockControl.createControl(HttpServletRequest.class);

然后，即可获得MockControl创建的Mock对象：

HttpServletRequest request = (HttpServletRequest)mc.getMock();



下一步，我们需要“录制”Mock对象的预期行为。在LoginServlet中，先后调用了 request.getParameter("username")和request.getParameter("password")两个方法，因此，需要在MockControl中设置这两次调用后的指定返回值。我们期望返回的值为“admin”和“1234”：

request.getParameter("username"); // 期望下面的测试将调用此方法，参数为"username"

mc.setReturnValue("admin", 1); // 期望返回值为"admin"，仅调用1次

request.getParameter("password"); // 期望下面的测试将调用此方法，参数为" password"

mc.setReturnValue("1234", 1); // 期望返回值为"1234"，仅调用1次

紧接着，调用mc.replay()，表示Mock对象“录制”完毕，可以开始按照我们设定的方式运行，我们对LoginServlet进行测试，并预期会产生一个RuntimeException：

LoginServletservlet=newLoginServlet();

 try{

 servlet.doPost(request,null);

 fail("Notcaughtexception!");

}

 catch(RuntimeExceptionre){

 assertEquals("Loginfailed.",re.getMessage());

}

 LoginServletservlet=newLoginServlet();

 try{

 servlet.doPost(request,null);

 fail("Notcaughtexception!");

}

 catch(RuntimeExceptionre){

 assertEquals("Loginfailed.",re.getMessage());

}

LoginServlet servlet = new LoginServlet(); try { servlet.doPost(request, null); fail("Not caught exception!"); } catch (RuntimeException re) { assertEquals("Login failed.", re.getMessage()); } LoginServlet servlet = new LoginServlet(); try { servlet.doPost(request, null); fail("Not caught exception!"); } catch (RuntimeException re) { assertEquals("Login failed.", re.getMessage()); } 由于本次测试的目的是检查当用户名和口令验证失败后，LoginServlet是否会抛出RuntimeException，因此，response对象对测试没有影响，我们不需要模拟它，仅仅传入null即可。



最后，调用mc.verify()检查Mock对象是否按照预期的方法调用正常运行了。



运行JUnit，测试通过！表示我们的Mock对象正确工作了！



下一步，我们来测试当用户名和口令匹配时，LoginServlet应当把请求转发给指定的RequestDispatcher。在这个测试用例中，我们除了需要HttpServletRequest Mock对象外，还需要模拟ServletContext和RequestDispatcher对象：

MockControlrequestCtrl=MockControl.createControl(HttpServletRequest.class);

HttpServletRequestrequestObj=(HttpServletRequest)requestCtrl.getMock();

 MockControlcontextCtrl=MockControl.createControl(ServletContext.class);

 finalServletContextcontextObj=(ServletContext)contextCtrl.getMock();

 MockControldispatcherCtrl=MockControl.createControl(RequestDispatcher.class);

RequestDispatcherdispatcherObj=(RequestDispatcher)dispatcherCtrl.getMock();

 MockControlrequestCtrl=MockControl.createControl(HttpServletRequest.class);

HttpServletRequestrequestObj=(HttpServletRequest)requestCtrl.getMock();

 MockControlcontextCtrl=MockControl.createControl(ServletContext.class);

 finalServletContextcontextObj=(ServletContext)contextCtrl.getMock();

 MockControldispatcherCtrl=MockControl.createControl(RequestDispatcher.class);

RequestDispatcherdispatcherObj=(RequestDispatcher)dispatcherCtrl.getMock();

按照doPost()的语句顺序，我们设定Mock对象指定的行为：

Java代码
 requestObj.getParameter("username");

 requestCtrl.setReturnValue("admin",1);

 requestObj.getParameter("password");

 requestCtrl.setReturnValue("123456",1);

 contextObj.getNamedDispatcher("dispatcher");

 contextCtrl.setReturnValue(dispatcherObj,1);

 dispatcherObj.forward(requestObj,null);

 dispatcherCtrl.setVoidCallable(1);

requestCtrl.replay();

contextCtrl.replay();

dispatcherCtrl.replay();

 requestObj.getParameter("username");

 requestCtrl.setReturnValue("admin",1);

 requestObj.getParameter("password");

 requestCtrl.setReturnValue("123456",1);

 contextObj.getNamedDispatcher("dispatcher");

 contextCtrl.setReturnValue(dispatcherObj,1);

 dispatcherObj.forward(requestObj,null);

 dispatcherCtrl.setVoidCallable(1);

requestCtrl.replay();

contextCtrl.replay();

dispatcherCtrl.replay();

MockControl requestCtrl = MockControl.createControl(HttpServletRequest.class); HttpServletRequest requestObj = (HttpServletRequest)requestCtrl.getMock(); MockControl contextCtrl = MockControl.createControl(ServletContext.class); final ServletContext contextObj = (ServletContext)contextCtrl.getMock(); MockControl dispatcherCtrl = MockControl.createControl(RequestDispatcher.class); RequestDispatcher dispatcherObj = (RequestDispatcher)dispatcherCtrl.getMock(); MockControl requestCtrl = MockControl.createControl(HttpServletRequest.class); HttpServletRequest requestObj = (HttpServletRequest)requestCtrl.getMock(); MockControl contextCtrl = MockControl.createControl(ServletContext.class); final ServletContext contextObj = (ServletContext)contextCtrl.getMock(); MockControl dispatcherCtrl = MockControl.createControl(RequestDispatcher.class); RequestDispatcher dispatcherObj = (RequestDispatcher)dispatcherCtrl.getMock(); 按照doPost()的语句顺序，我们设定Mock对象指定的行为： Java代码 requestObj.getParameter("username"); requestCtrl.setReturnValue("admin", 1); requestObj.getParameter("password"); requestCtrl.setReturnValue("123456", 1); contextObj.getNamedDispatcher("dispatcher"); contextCtrl.setReturnValue(dispatcherObj, 1); dispatcherObj.forward(requestObj, null); dispatcherCtrl.setVoidCallable(1); requestCtrl.replay(); contextCtrl.replay(); dispatcherCtrl.replay(); requestObj.getParameter("username"); requestCtrl.setReturnValue("admin", 1); requestObj.getParameter("password"); requestCtrl.setReturnValue("123456", 1); contextObj.getNamedDispatcher("dispatcher"); contextCtrl.setReturnValue(dispatcherObj, 1); dispatcherObj.forward(requestObj, null); dispatcherCtrl.setVoidCallable(1); requestCtrl.replay(); contextCtrl.replay(); dispatcherCtrl.replay();
然后，测试doPost()方法，这里，为了让getServletContext()方法返回我们创建的ServletContext Mock对象，我们定义一个匿名类并覆写getServletContext()方法：

LoginServletservlet=newLoginServlet(){

 publicServletContextgetServletContext(){

 returncontextObj;

}

};

 servlet.doPost(requestObj,null);

 LoginServletservlet=newLoginServlet(){

 publicServletContextgetServletContext(){

 returncontextObj;

}

};

LoginServlet servlet = new LoginServlet() { public ServletContext getServletContext() { return contextObj; } }; servlet.doPost(requestObj, null); LoginServlet servlet = new LoginServlet() { public ServletContext getServletContext() { return contextObj; } };servlet.doPost(requestObj, null);

最后，检查所有Mock对象的状态：

requestCtrl.verify();

contextCtrl.verify();

dispatcherCtrl.verify();

requestCtrl.verify();

contextCtrl.verify();

dispatcherCtrl.verify();

requestCtrl.verify(); contextCtrl.verify(); dispatcherCtrl.verify(); requestCtrl.verify(); contextCtrl.verify(); dispatcherCtrl.verify();
运行JUnit，测试通过！

倘若LoginServlet的代码有误，例如，将context.getNamedDispatcher("dispatcher")误写为 context.getNamedDispatcher("dispatcher2")，则测试失败，JUnit报告：

junit.framework.AssertionFailedError:

Unexpected method call getNamedDispatcher("dispatcher2"):

getNamedDispatcher("dispatcher2"): expected: 0, actual: 1

getNamedDispatcher("dispatcher"): expected: 1, actual: 0

at ...

完整的LoginServletTest代码如下：

Java代码
import javax.servlet.*;

import javax.servlet.http.*;

import org.easymock.*;

import junit.framework.TestCase;

public class LoginServletTest extends TestCase {

public void testLoginFailed() throws Exception {

MockControl mc = MockControl.createControl(HttpServletRequest.class);

HttpServletRequest request = (HttpServletRequest) mc.getMock();

// set Mock Object behavior:

request.getParameter("username");

mc.setReturnValue("admin", 1);

request.getParameter("password");

mc.setReturnValue("1234", 1);

// ok, all behaviors are set!

mc.replay();

// now start test:

LoginServlet servlet = new LoginServlet();

try {

servlet.doPost(request, null);

fail("Not caught exception!");

}

catch (RuntimeException re) {

assertEquals("Login failed.", re.getMessage());

}

// verify:

mc.verify();

}

public void testLoginOK() throws Exception {

// create mock:

MockControl requestCtrl = MockControl
.createControl(HttpServletRequest.class);

HttpServletRequest requestObj = (HttpServletRequest) requestCtrl
.getMock();

MockControl contextCtrl = MockControl
.createControl(ServletContext.class);

final ServletContext contextObj = (ServletContext) contextCtrl
.getMock();

MockControl dispatcherCtrl = MockControl
.createControl(RequestDispatcher.class);

RequestDispatcher dispatcherObj = (RequestDispatcher) dispatcherCtrl
.getMock();

// set behavior:

requestObj.getParameter("username");

requestCtrl.setReturnValue("admin", 1);

requestObj.getParameter("password");

requestCtrl.setReturnValue("123456", 1);

contextObj.getNamedDispatcher("dispatcher");

contextCtrl.setReturnValue(dispatcherObj, 1);

dispatcherObj.forward(requestObj, null);

dispatcherCtrl.setVoidCallable(1);

// done!

requestCtrl.replay();

contextCtrl.replay();

dispatcherCtrl.replay();

// test:

LoginServlet servlet = new LoginServlet() {

public ServletContext getServletContext() {

return contextObj;

}

};

servlet.doPost(requestObj, null);

// verify:

requestCtrl.verify();

contextCtrl.verify();

dispatcherCtrl.verify();

}

}

import javax.servlet.*;

import javax.servlet.http.*;

import org.easymock.*;

import junit.framework.TestCase;

public class LoginServletTest extends TestCase {

public void testLoginFailed() throws Exception {

MockControl mc = MockControl.createControl(HttpServletRequest.class);

HttpServletRequest request = (HttpServletRequest) mc.getMock();

// set Mock Object behavior:

request.getParameter("username");

mc.setReturnValue("admin", 1);

request.getParameter("password");

mc.setReturnValue("1234", 1);

// ok, all behaviors are set!

mc.replay();

// now start test:

LoginServlet servlet = new LoginServlet();

try {

servlet.doPost(request, null);

fail("Not caught exception!");

}

catch (RuntimeException re) {

assertEquals("Login failed.", re.getMessage());

}

// verify:

mc.verify();

}

public void testLoginOK() throws Exception {

// create mock:

MockControl requestCtrl = MockControl
.createControl(HttpServletRequest.class);

HttpServletRequest requestObj = (HttpServletRequest) requestCtrl
.getMock();

MockControl contextCtrl = MockControl
.createControl(ServletContext.class);

final ServletContext contextObj = (ServletContext) contextCtrl
.getMock();

MockControl dispatcherCtrl = MockControl
.createControl(RequestDispatcher.class);

RequestDispatcher dispatcherObj = (RequestDispatcher) dispatcherCtrl
.getMock();

// set behavior:

requestObj.getParameter("username");

requestCtrl.setReturnValue("admin", 1);

requestObj.getParameter("password");

requestCtrl.setReturnValue("123456", 1);

contextObj.getNamedDispatcher("dispatcher");

contextCtrl.setReturnValue(dispatcherObj, 1);

dispatcherObj.forward(requestObj, null);

dispatcherCtrl.setVoidCallable(1);

// done!

requestCtrl.replay();

contextCtrl.replay();

dispatcherCtrl.replay();

// test:

LoginServlet servlet = new LoginServlet() {

public ServletContext getServletContext() {

return contextObj;

}

};

servlet.doPost(requestObj, null);

// verify:

requestCtrl.verify();

contextCtrl.verify();

dispatcherCtrl.verify();

}

}
总结：

虽然EasyMock可以用来模仿依赖对象，但是，它只能动态模仿接口，无法模仿具体类。这一限制正好要求我们遵循“针对接口编程”的原则：如果不针对接口，则测试难于进行。应当把单元测试看作是运行时代码的最好运用，如果代码在单元测试中难于应用，则它在真实环境中也将难于应用。总之，创建尽可能容易测试的代码就是创建高质量的代码。

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