Moq验证失败：已调用AttemptToCreateUser但单元测试不通过

我正在测试注册接口的RegisterUser方法，核心目标是验证this.userService.AttemptToCreateUser(newUser, registerDto.Password)是否被调用。但测试执行后失败，错误信息显示预期调用1次但实际0次，可“已执行调用”部分明明显示该方法用相同参数被调用过了。

注册接口实现代码 #

[HttpPost("Register")]
public async Task<ActionResult<UserDto>> RegisterUser([FromBody] RegisterDto registerDto)
{
    _logger.Info($"Register user end point hit. Username {registerDto.Username}");

    await validationService.Validate(registerDto);

    if (!await this.userService.CheckUserDoesNotAlreadyExistByName(registerDto.Username))
    {
        throw new ValidationException("Username already exists");
    }
    
    if(!await this.userService.CheckUserDoesNotAlreadyExistByEmail(registerDto.Email))
    {
        throw new ValidationException("Email already exists");
    }

    _logger.Info($"Register dto model validation complete. Attempting to create user. Username: {registerDto.Username}. Email: {registerDto.Email}");

    var newUser = this.mapper.Map<AppUser>(registerDto);

    var result = await this.userService.AttemptToCreateUser(newUser, registerDto.Password);

    if (!result.Succeeded)
    {
        AggregateException aggregateException = this.userService.HandleUnsuccessfulUserCreation(result.Errors);
        throw aggregateException;
    }
    else
    {
        return Ok(await this.userService.HandleSuccessfulUserCreation(newUser));
    }
}            

单元测试代码 #

[Fact]
public async void RegisterUser_should_call_user_service_AttemptToCreateUser_method()
{
    //arrange 
    var registerDto = MockRegisterDtoGenerator.GenerateMockRegisterDto();
    var appUser = MockUserGenerator.GenerateMockUser();
    var mockUserService = MockUserServiceGenerator.GenerateMockUserService(appUser);
    var sut = AccountControllerGenerator.CreateAccountController(mockUserService.Object);

    //Act 
    await sut.RegisterUser(registerDto);

    //assert
    mockUserService.Verify(x => x.AttemptToCreateUser(appUser, registerDto.Password), Times.Once);
}

MockUserService生成方法 #

internal static Mock<IUserService> GenerateMockUserService(AppUser mockUser)
{
    var userTask = Task.FromResult(mockUser);
    var mockUserService = new Mock<IUserService>();
    var identityResult = IdentityResult.Success;
    var identityResultTask = Task.FromResult(identityResult);
    mockUserService.Setup(x => x.UpdateUser(It.IsAny<AppUser>())).Returns(identityResultTask);
    mockUserService.Setup(x => x.AttemptToCreateUser(It.IsAny<AppUser>(), It.IsAny<string>())).Returns(identityResultTask);
    mockUserService.Setup(x => x.FindByIdAsync(It.IsAny<int>())).Returns(userTask);
    mockUserService.Setup(x => x.CheckUserDoesNotAlreadyExistByEmail(It.IsAny<string>(), It.IsAny<CancellationToken>())).Returns(Task.FromResult(true));
    mockUserService.Setup(x => x.CheckUserDoesNotAlreadyExistByName(It.IsAny<string>(), It.IsAny<CancellationToken>())).Returns(Task.FromResult(true));
    return mockUserService;
}

测试错误信息 #

Moq.MockException : Expected invocation on the mock once, but was 0 times: x => x.AttemptToCreateUser(Mr Test, "Pa$$w0rd")

Configured setups: x => x.AttemptToCreateUser(It.IsAny(), It.IsAny()), Times.Once

Performed invocations:

IUserService.CheckUserDoesNotAlreadyExistByName("Mr Test", System.Threading.CancellationToken)

IUserService.CheckUserDoesNotAlreadyExistByEmail("TestEmail@gmail.com", System.Threading.CancellationToken)

IUserService.AttemptToCreateUser(Mr Test, "Pa$$w0rd")

IUserService.HandleSuccessfulUserCreation(Mr Test)

原因分析 #

问题出在Moq的参数匹配逻辑上：
你在验证时传入的appUser是测试代码里MockUserGenerator.GenerateMockUser()创建的实例，但控制器中调用this.mapper.Map<AppUser>(registerDto)生成的newUser是另一个全新的AppUser对象。虽然两个对象的属性（用户名、邮箱等）完全一致，但它们是内存中两个不同的引用实例。

Moq默认使用引用相等来匹配对象参数，所以它认为验证时的appUser和实际调用时的newUser不是同一个参数，因此判定“未调用”。

解决方案 #

有两种常用的解决方式：

方式1：基于属性值匹配参数 #

修改验证逻辑，不直接用引用对象，而是通过属性值来匹配AppUser参数：

mockUserService.Verify(x => x.AttemptToCreateUser(
    It.Is<AppUser>(u => u.Username == appUser.Username && u.Email == appUser.Email),
    registerDto.Password), 
Times.Once);

这种方式只关心对象的属性是否符合预期，不要求是同一个引用实例。

方式2：让Mapper返回测试用的appUser实例 #

如果需要严格验证确实是某个特定实例被传入，可以Mock控制器依赖的IMapper，让它在调用Map<AppUser>(registerDto)时返回你测试中创建的appUser：

1. 在测试的Arrange阶段添加Mock的Mapper：

var mockMapper = new Mock<IMapper>();
mockMapper.Setup(m => m.Map<AppUser>(registerDto)).Returns(appUser);

2. 创建控制器时把这个Mock的Mapper传入（需要修改AccountControllerGenerator.CreateAccountController方法，支持传入Mapper参数）。

这样控制器中生成的newUser就是测试里的appUser实例，Moq的引用匹配就能通过。

内容的提问来源于stack exchange，提问作者Pablo52