私有方法测试策略：行为驱动的间接验证与最佳实践

public class UserService {      private UserRepository userRepository; // 假设通过构造函数注入      public UserService(UserRepository userRepository) {         this.userRepository = userRepository;     }      public User create(User user) {         checkUsername(user.getUsername());         return userRepository.save(user);     }      private void checkUsername(String username) {         if (username.equals("dummy")) {             String msg = String.format("Username = '%s' is cannot be used!", username);             throw new UsernameUnavailableException(msg);         } else if (userRepository.existsByUsername(username)) {             String msg = String.format("Username = '%s' is being used by another user!", username);             throw new UsernameIsInUseException(msg);         }         // 如果用户名不存在且不为"dummy"，则继续     } }

import org.junit.jupiter.api.BeforeEach; import org.junit.jupiter.api.Test; import org.mockito.InjectMocks; import org.mockito.Mock; import org.mockito.MockitoAnnotations;  import static org.junit.jupiter.api.Assertions.*; import static org.mockito.Mockito.*;  public class UserServiceTest {      @Mock     private UserRepository userRepository; // 模拟 UserRepository      @InjectMocks     private UserService userService; // 注入模拟对象到 UserService      @BeforeEach     void setUp() {         MockitoAnnotations.openMocks(this); // 初始化模拟对象     }      @Test     void create_shouldThrowUsernameUnavailableException_whenUsernameIsDummy() {         // 1. 设置模拟行为 (此场景下，userRepository的方法不应被调用)         // doNothing().when(userRepository).existsByUsername(anyString()); // 可以选择不设置，因为期望不被调用          // 2. 执行待测方法         User dummyUser = new User("dummy", "password");         UsernameUnavailableException exception = assertThrows(                 UsernameUnavailableException.class,                 () -> userService.create(dummyUser)         );          // 3. 验证结果和交互         assertEquals("Username = 'dummy' is cannot be used!", exception.getMessage());         // 验证 userRepository 的方法未被调用         verify(userRepository, never()).existsByUsername(anyString());         verify(userRepository, never()).save(any(User.class));     }      @Test     void create_shouldThrowUsernameIsInUseException_whenUsernameAlreadyExists() {         // 1. 设置模拟行为：当调用 existsByUsername("existingUser") 时返回 true         when(userRepository.existsByUsername("existingUser")).thenReturn(true);          // 2. 执行待测方法         User existingUser = new User("existingUser", "password");         UsernameIsInUseException exception = assertThrows(                 UsernameIsInUseException.class,                 () -> userService.create(existingUser)         );          // 3. 验证结果和交互         assertEquals("Username = 'existingUser' is being used by another user!", exception.getMessage());         // 验证 existsByUsername 被调用一次，save 未被调用         verify(userRepository, times(1)).existsByUsername("existingUser");         verify(userRepository, never()).save(any(User.class));     }      @Test     void create_shouldSaveUserSuccessfully_whenUsernameIsValidAndUnique() {         // 1. 设置模拟行为：当调用 existsByUsername("newUser") 时返回 false，         //    当调用 save(any(User.class)) 时返回传入的用户对象         User newUser = new User("newUser", "password");         when(userRepository.existsByUsername("newUser")).thenReturn(false);         when(userRepository.save(any(User.class))).thenReturn(newUser);          // 2. 执行待测方法         User savedUser = userService.create(newUser);          // 3. 验证结果和交互         assertNotNull(savedUser);         assertEquals("newUser", savedUser.getUsername());         // 验证 existsByUsername 和 save 都被调用一次         verify(userRepository, times(1)).existsByUsername("newUser");         verify(userRepository, times(1)).save(any(User.class));     }      // 假设 User 类和 UserRepository 接口定义如下     static class User {         String username;         String password;         // 构造函数、getter/setter         public User(String username, String password) {             this.username = username;             this.password = password;         }         public String getUsername() { return username; }         public void setUsername(String username) { this.username = username; }         public String getPassword() { return password; }         public void setPassword(String password) { this.password = password; }     }      interface UserRepository {         boolean existsByUsername(String username);         User save(User user);     }      // 假设异常类定义如下     static class UsernameUnavailableException extends RuntimeException {         public UsernameUnavailableException(String message) { super(message); }     }     static class UsernameIsInUseException extends RuntimeException {         public UsernameIsInUseException(String message) { super(message); }     } }

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