如何使用 Moq 对 .NET 微服务进行单元测试？

public interface IUserRepository
{
    Task<User> GetByIdAsync(int id);
}

public class OrderService
{
    private readonly IUserRepository _userRepository;

    public OrderService(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }

    public async Task<bool> CanPlaceOrder(int userId)
    {
        var user = await _userRepository.GetByIdAsync(userId);
        return user != null && user.IsActive;
    }
}

[Fact]
public async Task CanPlaceOrder_WhenUserIsActive_ReturnsTrue()
{
    // Arrange
    var mockRepo = new Mock<IUserRepository>();
    mockRepo.Setup(x => x.GetByIdAsync(1))
            .ReturnsAsync(new User { Id = 1, IsActive = true });

    var service = new OrderService(mockRepo.Object);

    // Act
    var result = await service.CanPlaceOrder(1);

    // Assert
    Assert.True(result);
}

public interface ILogger
{
    void Log(string message);
}

// 在 OrderService 中新增方法
public async Task PlaceOrder(int userId)
{
    if (await CanPlaceOrder(userId))
    {
        _logger.Log($"Order placed by user {userId}");
    }
}

[Fact]
public async Task PlaceOrder_WhenValid_CallsLogger()
{
    // Arrange
    var mockRepo = new Mock<IUserRepository>();
    var mockLogger = new Mock<ILogger>();

    mockRepo.Setup(x => x.GetByIdAsync(1)).ReturnsAsync(new User { Id = 1, IsActive = true });

    var service = new OrderService(mockRepo.Object, mockLogger.Object);

    // Act
    await service.PlaceOrder(1);

    // Assert
    mockLogger.Verify(x => x.Log(It.Is<string>(s => s.Contains("Order placed"))), Times.Once);
}

mockRepo.Setup(x => x.GetByIdAsync(It.IsAny<int>()))
        .ReturnsAsync((int id) => new User { Id = id, IsActive = id % 2 == 0 });