// Method_Scenario_Expected
[Fact]
public async Task GetUser_ExistingId_ReturnsUser()
{
    // Arrange
    var repo = new Mock<IUserRepository>();
    repo.Setup(r => r.FindAsync(1))
        .ReturnsAsync(new User { Id = 1, Name = "Alice" });
    var service = new UserService(repo.Object);

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

    // Assert
    Assert.NotNull(result);
    Assert.Equal("Alice", result.Name);
}

[Fact]
public async Task GetUser_NonExistentId_ReturnsNull()
{
    // Arrange
    var repo = new Mock<IUserRepository>();
    repo.Setup(r => r.FindAsync(99)).ReturnsAsync((User?)null);
    var service = new UserService(repo.Object);

    // Act
    var result = await service.GetUserAsync(99);

    // Assert
    Assert.Null(result);
}