تست نویسی با xUnit در Asp.Net Core

public class UserService : IUserService
{
    private readonly IUserRepository _userRepository;

    public UserService(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }
    public async Task<int> AverageUsersAge()
    {
        int result = 0;
        var people = await _userRepository.GetAllUsers();
        if (people is null)
            return result;

        result = (int)people.Select(a => a.Age).DefaultIfEmpty().Average();
        return result;
    }
}

<ItemGroup>
  <PackageReference Include="FluentAssertions" Version="6.2.0" />
  <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
  <PackageReference Include="Moq" Version="4.16.1" />
  <PackageReference Include="xunit" Version="2.4.1" />
  <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3"/>
</ItemGroup>

public class UserServiceTest
{
    private readonly IUserService _userService;
    private readonly Mock<IUserRepository> _userRepository;
    public UserServiceTest()
    {
        _userRepository = new Mock<IUserRepository>();
        _userService = new UserService(_userRepository.Object);
    }
}

[Fact]
public async Task AverageUsersAge_When_Repository_Return_Null_Then_Zero_Should_Be_Returned()
{
    _userRepository.Setup(a => a.GetAllUsers())
        .ReturnsAsync((List<User>)null);

    var result = await _userService.AverageUsersAge();

    result.Should().Be(0);
}

[Fact]
public async Task AverageUsersAge_When_Repository_Return_Empty_Then_Zero_Should_Be_Returned()
{
    _userRepository.Setup(a => a.GetAllUsers())
        .ReturnsAsync(new List<User>());

    var result = await _userService.AverageUsersAge();

    result.Should().Be(0);
}

[Fact]
public async Task AverageUsersAge_When_Repository_Return_List_Of_Users_Then_Average_Of_Age_Should_Be_Retunred()
{

    _userRepository.Setup(a => a.GetAllUsers())
        .ReturnsAsync(UserMockData.People);

    var result = await _userService.AverageUsersAge();

    var expected = (UserMockData.AdultUser.Age + UserMockData.ChildUser.Age + UserMockData.InfantUser.Age) / 3;

    result.Should().Be(expected);
}

public static class UserMockData
 {
     public static List<User> People
     {
         get
         {
             return new List<User>
             {
                 AdultUser,
                 ChildUser,
                 InfantUser
             };
         }
     }
     public static User AdultUser
     {
         get
         {
             return new User
             {
                 Age = 55
             };
         }
     }
     public static User ChildUser
     {
         get
         {
             return new User
             {
                 Age = 10
             };
         }
     }
     public static User InfantUser
     {
         get
         {
             return new User
             {
                 Age = 2
             };
         }
     }
 }