So I'm trying to learn unit testing in C# with a sample project I found online. The project is here.

This is my first time doing unit testing so, I am still learning and have come across some errors. Here is the code I am trying to test:

IRoosterService:

namespace MoqBusiness
{    
    public interface IRoosterService
    {
        IList<Player> GetPlayersFromRepo();
    }
}

RoosterService:

namespace MoqBusiness
{
    public class RoosterService : IRoosterService
    {
        private readonly IPlayersRepo _players;

        public RoosterService(IPlayersRepo players)
        {
            _players = players;
        }
        
        public IList<Player> GetPlayersFromRepo()
        {
            return _players.GetPlayerList();
        }
    }
}

IPlayersRepo:

namespace MoqDataRepos
{
    public interface IPlayersRepo
    {
        IList<Player> GetPlayerList();
    }
}

PlayersRepo:

namespace MoqDataRepos
{
    public class PlayersRepo:IPlayersRepo
    { 
        public IList<Player> GetPlayerList()
        {
            var playerList = new List<Player> {
                new Player { Name = "Swaroop", Age = 28 ,PlayersClub = new Club{ ClubName = "Manchester United",CountryName = "GB",Position = 7} },
                new Player { Name = "Seema", Age = 30 ,PlayersClub = new Club{ ClubName = "Manchester United",CountryName = "GB",Position = 7}},
                new Player { Name = "Jay", Age = 35 ,PlayersClub = new Club{ ClubName = "Arsenal",CountryName = "GB",Position = 4}},
                new Player { Name = "Don", Age = 30 ,PlayersClub = new Club{ ClubName = "Manchester City",CountryName = "GB",Position = 1}}
            };
            return playerList;
        }
    }
}

So I am trying to test this RoosterService class to start with, using Moq and XUnit.

My thinking was I am testing to see if the GetPlayersFromRepo method returns the players that are in PlayersRepo - GetPlayerList so I would first use GetPlayersFromRepo method, then call PlayersRepo - GetPlayerList method and compare the two to see if they are equal.

Here is my code for this Test:

namespace MoqTests
{
    public class RoosterServiceTests
    {
        private readonly RoosterService _service;
        private readonly Mock<IPlayersRepo> playersRepoMock = new Mock<IPlayersRepo>();

        public RoosterServiceTests()
        {
            _service = new RoosterService(playersRepoMock.Object);
        }
        
        [Fact]
        public void GetPlayersFromRepo_ShouldReturnPlayers()
        {
            //Arrange
            var expected = playersRepoMock.Setup(p => p.GetPlayerList()).Returns(new List<Player>());
            
            //Act
            var players = _service.GetPlayersFromRepo();

            //Assert
            Assert.Equal(players, expected);
        }

    }
}

However this does not work as the following error message comes up

Argument 2: cannot convert from 'Moq.Language.Flow.IReturnsResult<MoqDataRepos.IPlayersRepo>' to 'System.Collections.Generic.IEnumerable<MoqDataModel.Player>'

I don't understand why this is happening as both methods return a list so not sure why this error occurs. Since this is my first test I guess I may be setting it up wrong too? Any advice appreciated.

CodePudding user response：

First, you don't need the return value of playersRepoMock.Setup and what it's returning is probably not what you're expecting.

Second, in your unit test, you'll have something like this:

[Fact]
public void GetPlayersFromRepo_ShouldReturnPlayers()
{
    //Arrange
    var expected = new List<Player>();
    playersRepoMock.Setup(p => p.GetPlayerList()).Returns(expected);
            
    //Act
    var players = _service.GetPlayersFromRepo();

    //Assert
    Assert.Equal(expected, players);
}

CodePudding user response：

I would suggest to do the followings:

• Naming
  • Use the Given When Then structure to describe the test cases
  • Use the expected and actual prefixes to help legibility
  • Use System Under Test (or in short sut) as a variable name for that object which is being tested
• Technical ones
  • Prefer to use non-empty collections for happy path tests
    • Empty collections are usually considered edge or corner cases
  • Make sure that your mocked object is being called as intended (Verify)
  • Recreate your mock object(s) in every test cases to make them isolated (F.I.R.S.T. principles)

[Fact]
public void GivenAPlayerListWithASinglePlayer_WhenICallGetPlayersFromRepo_ThenItReturnsTheReposCollection()
{
    //Arrange
    var club = new Club { ClubName = "Manchester United", CountryName = "GB", Position = 7 };
    var player = new Player { Name = "Swaroop", Age = 28 ,PlayersClub =  club };
    var expectedPlayers = new List<Player> { player };

    var playersRepoMock = new Mock<IPlayersRepo>();
    playersRepoMock
       .Setup(p => p.GetPlayerList())
       .Returns(expectedPlayers);

    var sut = new RoosterService(playersRepoMock.Object);
    
    //Act
    var actualPlayers = sut.GetPlayersFromRepo();

    //Assert
    playersRepoMock.Verify(p => p.GetPlayerList(), Times.Once);
    Assert.Equal(expectedPlayers, actualPlayers);
}

Depending on the fact how defensively you want to test your code you can have the following test cases:

• Make sure that no new player has been added to the list
• Make sure that no existing player has been removed from the list
• Make sure that no player or club information is altered/tampered
• Make sure that the players' order is unchanged
• etc.

P.S.: If you need to perform assertions against collection then please prefer to use the FluentAssertions