Mockito vs EasyMock vs JMockit：Java 主流 Mock 框架对比

最后修改:2024年1月8日

by baeldung

1. 简介

1.1. 概述

这篇文章将讨论 Mock 测试 的基本概念、使用原因，并通过一个统一的测试场景，分别使用 Mockito、EasyMock 和 JMockit 这三个主流 Java Mock 框架进行实现，从而帮助你更直观地比较它们的用法和优劣。

我们会从 Mock 的基本概念入手，接着定义一个通用的测试用例，然后分别用三个框架实现，最后给出对比结论。如果你已经对 Mock 有所了解，可以直接跳到第 2 节。

1.2. 为什么使用 Mock

假设你已经在使用 TDD、ATDD 或 BDD 等以测试为中心的开发方式，或者你正在为一个已有类编写测试。在对某个类进行单元测试时，我们只关心它本身的行为，而不是它依赖的其他组件。

为了实现这一点，我们需要用 可控的替代对象 来替换真实依赖。这样可以强制返回特定值、抛出异常，或者跳过耗时操作。这种替代对象就是 Mock 对象，它可以帮助我们简化测试代码并提升执行效率。

1.3. Mock 相关术语定义

Martin Fowler 的 这篇文章 很好地总结了 Mock 的基本概念：

  • Dummy：用于填充参数列表的对象，但不会被实际使用。
  • Fake：拥有实际功能实现的对象，但通常走的是捷径，不适合生产环境（如内存数据库）。
  • Stub：为测试提供预设返回值的对象，通常不处理预设之外的调用。也可以记录调用信息。
  • Mock：我们这里讨论的对象，预先设定好期望行为，用于验证是否被正确调用。

1.4. 是否需要 Mock：这是个问题

并不是所有对象都需要 Mock。有时候直接做集成测试比 Mock 更有价值。比如我们要测试的 LoginDao，它依赖第三方数据库库。Mock 它只能验证参数是否准备正确，但无法验证实际数据库返回是否符合预期。

因此，本文将不对 LoginDao 进行 Mock，而是直接使用真实调用（虽然也可以同时写单元测试和集成测试）。

2. 测试用例

2.1. 用例说明

我们将使用一个典型的分层架构登录流程作为测试用例：

  1. Controller 接收登录请求
  2. Service 层处理业务逻辑
  3. DAO 层访问数据库验证用户信息

我们将重点测试各组件之间的交互，而不是具体实现。

结构图如下：

Test case diagram

2.2. 实现代码

用户表单类 UserForm

public class UserForm {
    public String password;
    public String username;
    public String getUsername() {
        return username;
    }
}

数据访问类 LoginDao

public class LoginDao {
    public int login(UserForm userForm) {
        return 0;
    }
}

服务类 LoginService

public class LoginService {
    private LoginDao loginDao;
    private String currentUser;

    public boolean login(UserForm userForm) {
        assert null != userForm;
        int loginResults = loginDao.login(userForm);
        switch (loginResults) {
            case 1:
                return true;
            default:
                return false;
        }
    }

    public void setCurrentUser(String username) {
        if (null != username) {
            this.currentUser = username;
        }
    }
}

控制器类 LoginController

public class LoginController {
    public LoginService loginService;

    public String login(UserForm userForm) {
        if (null == userForm) {
            return "ERROR";
        } else {
            boolean logged;

            try {
                logged = loginService.login(userForm);
            } catch (Exception e) {
                return "ERROR";
            }

            if (logged) {
                loginService.setCurrentUser(userForm.getUsername());
                return "OK";
            } else {
                return "KO";
            }
        }
    }
}

3. 测试环境搭建

3.1. Mockito

使用版本：2.8.9

常用注解：

  • @Mock：创建 Mock 对象
  • @InjectMocks：注入 Mock 对象到被测试对象
  • @Spy：创建部分 Mock（保留真实实现）
public class LoginControllerTest {

    @Mock
    private LoginDao loginDao;

    @Spy
    @InjectMocks
    private LoginService spiedLoginService;

    @Mock
    private LoginService loginService;

    @InjectMocks
    private LoginController loginController;

    @Before
    public void setUp() {
        loginController = new LoginController();
        MockitoAnnotations.initMocks(this);
    }
}

3.2. EasyMock

使用版本：3.4

使用 @RunWith(EasyMockRunner.class) 简化测试：

@RunWith(EasyMockRunner.class)
public class LoginControllerTest {

    @Mock
    private LoginDao loginDao;

    @Mock
    private LoginService loginService;

    @TestSubject
    private LoginController loginController = new LoginController();
}

3.3. JMockit

使用版本：1.49

使用注解：

  • @Injectable：创建单个 Mock 实例
  • @Mocked：Mock 所有实例
  • @Tested：创建被测试对象并自动注入 Mock
public class LoginControllerIntegrationTest {

    @Injectable
    private LoginDao loginDao;

    @Injectable
    private LoginService loginService;

    @Tested
    private LoginController loginController;
}

4. 验证 Mock 未被调用

4.1. Mockito

@Test
public void assertThatNoMethodHasBeenCalled() {
    loginController.login(null);
    Mockito.verifyNoInteractions(loginService);
}

4.2. EasyMock

@Test
public void assertThatNoMethodHasBeenCalled() {
    EasyMock.replay(loginService);
    loginController.login(null);
    EasyMock.verify(loginService);
}

4.3. JMockit

@Test
public void assertThatNoMethodHasBeenCalled() {
    loginController.login(null);
    new FullVerifications(loginService) {};
}

5. 定义 Mock 行为并验证调用

5.1. Mockito

@Test
public void assertTwoMethodsHaveBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    Mockito.when(loginService.login(userForm)).thenReturn(true);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    Mockito.verify(loginService).login(userForm);
    Mockito.verify(loginService).setCurrentUser("foo");
}

@Test
public void assertOnlyOneMethodHasBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    Mockito.when(loginService.login(userForm)).thenReturn(false);

    String login = loginController.login(userForm);

    Assert.assertEquals("KO", login);
    Mockito.verify(loginService).login(userForm);
    Mockito.verifyNoMoreInteractions(loginService);
}

5.2. EasyMock

@Test
public void assertTwoMethodsHaveBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    EasyMock.expect(loginService.login(userForm)).andReturn(true);
    loginService.setCurrentUser("foo");
    EasyMock.replay(loginService);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    EasyMock.verify(loginService);
}

@Test
public void assertOnlyOneMethodHasBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    EasyMock.expect(loginService.login(userForm)).andReturn(false);
    EasyMock.replay(loginService);

    String login = loginController.login(userForm);

    Assert.assertEquals("KO", login);
    EasyMock.verify(loginService);
}

5.3. JMockit

@Test
public void assertTwoMethodsHaveBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    new Expectations() {{
        loginService.login(userForm); result = true;
        loginService.setCurrentUser("foo");
    }};

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    new FullVerifications(loginService) {};
}

@Test
public void assertOnlyOneMethodHasBeenCalled() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    new Expectations() {{
        loginService.login(userForm); result = false;
        // no expectation for setCurrentUser
    }};

    String login = loginController.login(userForm);

    Assert.assertEquals("KO", login);
    new FullVerifications(loginService) {};
}

6. Mock 抛出异常

6.1. Mockito

@Test
public void mockExceptionThrowing() {
    UserForm userForm = new UserForm();
    Mockito.when(loginService.login(userForm)).thenThrow(IllegalArgumentException.class);

    String login = loginController.login(userForm);

    Assert.assertEquals("ERROR", login);
    Mockito.verify(loginService).login(userForm);
    Mockito.verifyNoInteractions(loginService);
}

6.2. EasyMock

@Test
public void mockExceptionThrowing() {
    UserForm userForm = new UserForm();
    EasyMock.expect(loginService.login(userForm)).andThrow(new IllegalArgumentException());
    EasyMock.replay(loginService);

    String login = loginController.login(userForm);

    Assert.assertEquals("ERROR", login);
    EasyMock.verify(loginService);
}

6.3. JMockit

@Test
public void mockExceptionThrowing() {
    UserForm userForm = new UserForm();
    new Expectations() {{
        loginService.login(userForm); result = new IllegalArgumentException();
        // no expectation for setCurrentUser
    }};

    String login = loginController.login(userForm);

    Assert.assertEquals("ERROR", login);
    new FullVerifications(loginService) {};
}

7. Mock 传递对象

7.1. Mockito

@Test
public void mockAnObjectToPassAround() {
    UserForm userForm = Mockito.when(Mockito.mock(UserForm.class).getUsername())
      .thenReturn("foo").getMock();
    Mockito.when(loginService.login(userForm)).thenReturn(true);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    Mockito.verify(loginService).login(userForm);
    Mockito.verify(loginService).setCurrentUser("foo");
}

7.2. EasyMock

@Test
public void mockAnObjectToPassAround() {
    UserForm userForm = EasyMock.mock(UserForm.class);
    EasyMock.expect(userForm.getUsername()).andReturn("foo");
    EasyMock.expect(loginService.login(userForm)).andReturn(true);
    loginService.setCurrentUser("foo");
    EasyMock.replay(userForm);
    EasyMock.replay(loginService);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    EasyMock.verify(userForm);
    EasyMock.verify(loginService);
}

7.3. JMockit

@Test
public void mockAnObjectToPassAround(@Mocked UserForm userForm) {
    new Expectations() {{
        userForm.getUsername(); result = "foo";
        loginService.login(userForm); result = true;
        loginService.setCurrentUser("foo");
    }};
    
    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    new FullVerifications(loginService) {};
    new FullVerifications(userForm) {};
}

8. 自定义参数匹配

8.1. Mockito

@Test
public void argumentMatching() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    // default matcher
    Mockito.when(loginService.login(Mockito.any(UserForm.class))).thenReturn(true);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    Mockito.verify(loginService).login(userForm);
    // complex matcher
    Mockito.verify(loginService).setCurrentUser(ArgumentMatchers.argThat(
        new ArgumentMatcher<String>() {
            @Override
            public boolean matches(String argument) {
                return argument.startsWith("foo");
            }
        }
    ));
}

8.2. EasyMock

@Test
public void argumentMatching() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    // default matcher
    EasyMock.expect(loginService.login(EasyMock.isA(UserForm.class))).andReturn(true);
    // complex matcher
    loginService.setCurrentUser(specificArgumentMatching("foo"));
    EasyMock.replay(loginService);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    EasyMock.verify(loginService);
}

private static String specificArgumentMatching(String expected) {
    EasyMock.reportMatcher(new IArgumentMatcher() {
        @Override
        public boolean matches(Object argument) {
            return argument instanceof String 
              && ((String) argument).startsWith(expected);
        }

        @Override
        public void appendTo(StringBuffer buffer) {
            //NOOP
        }
    });
    return null;
}

8.3. JMockit

@Test
public void argumentMatching() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    // default matcher
    new Expectations() {{
        loginService.login((UserForm) any);
        result = true;
        // complex matcher
        loginService.setCurrentUser(with(new Delegate<String>() {
            @Override
            public boolean matches(Object item) {
                return item instanceof String && ((String) item).startsWith("foo");
            }
        }));
    }};

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    new FullVerifications(loginService) {};
}

9. 部分 Mock（Partial Mocking）

9.1. Mockito

@Test
public void partialMocking() {
    // use partial mock
    loginController.loginService = spiedLoginService;
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    // let service's login use implementation so let's mock DAO call
    Mockito.when(loginDao.login(userForm)).thenReturn(1);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    // verify mocked call
    Mockito.verify(spiedLoginService).setCurrentUser("foo");
}

9.2. EasyMock

@Test
public void partialMocking() {
    UserForm userForm = new UserForm();
    userForm.username = "foo";
    // use partial mock
    LoginService loginServicePartial = EasyMock.partialMockBuilder(LoginService.class)
      .addMockedMethod("setCurrentUser").createMock();
    loginServicePartial.setCurrentUser("foo");
    // let service's login use implementation so let's mock DAO call
    EasyMock.expect(loginDao.login(userForm)).andReturn(1);

    loginServicePartial.setLoginDao(loginDao);
    loginController.loginService = loginServicePartial;
    
    EasyMock.replay(loginDao);
    EasyMock.replay(loginServicePartial);

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    // verify mocked call
    EasyMock.verify(loginServicePartial);
    EasyMock.verify(loginDao);
}

9.3. JMockit

@Test
public void partialMocking() {
    LoginService partialLoginService = new LoginService();
    partialLoginService.setLoginDao(loginDao);
    loginController.loginService = partialLoginService;

    UserForm userForm = new UserForm();
    userForm.username = "foo";
        
    new Expectations(partialLoginService) {{
        // let's mock DAO call
        loginDao.login(userForm); result = 1;
            
        // no expectation for login method so that real implementation is used
            
        // mock setCurrentUser call
        partialLoginService.setCurrentUser("foo");
    }};

    String login = loginController.login(userForm);

    Assert.assertEquals("OK", login);
    // verify mocked call
    new Verifications() {{
        partialLoginService.setCurrentUser("foo");
    }};     
}

10. 总结

在这篇文章中，我们比较了三种主流的 Java Mock 框架：

✅ 配置易用性：三者都支持注解，但 Mockito 和 JMockit 更简洁
✅ 结构清晰度：JMockit 强制使用 Expectations 和 Verifications 块，结构最清晰
✅ 语法一致性：JMockit 的 result = ... 语法适用于正常返回和异常抛出
✅ 社区支持：Mockito 仍是最多人使用的，生态更成熟
❌ EasyMock 需要手动 replay：这是个明显的缺点
✅ 部分 Mock：三者都支持，JMockit 实现最自然

综合来看，我们推荐 JMockit 作为首选 Mock 框架，尽管我们过去常用 Mockito。它的结构清晰、语法一致，非常适合构建高质量的测试代码。

完整代码可在 GitHub 获取。

原始标题:Mockito vs EasyMock vs JMockit

« 上一篇： 使用 Guava 将 Set 转换为 Map 的三种实现方式
» 下一篇： 在Spring REST API中使用Protocol Buffers