将模拟方法的结果返回到另一个模拟方法

Question

I've got a class that has the following implementation:

public sealed class HotelRepository : IHotelRepository
{
    private readonly string _dataSource;

    public HotelRepository(string dataSource) => _dataSource = dataSource;

    /// <inheritdoc />
    public async Task<IEnumerable<Hotel>> GetAllAsync() =>
        await Task.Run(() => JObject.Parse(File.ReadAllText(_dataSource))["hotels"].ToList().Select(x => x.ToObject<Hotel>()));

    /// <inheritdoc />
    public async Task<IEnumerable<Hotel>> GetListByMatchAsync(string name) =>
        await GetAllAsync().ContinueWith(x => x.Result.Where(y => y.Name.Contains(name, StringComparison.CurrentCultureIgnoreCase)));
}

As you can see, the GetListByMatchAsync method calls GetAllAsync , then does some logic before returning the result.

When I tried to mock this repository for unit testing, I'm struggling to get a result out of GetListByMatchAsync as it always fails as a null reference exception.

Here's the unit test:

[TestCase("Test", "X")]
[TestCase("Hotel", "X")]
[TestCase("Name", "X")]
public async Task GetListByMatchAsync_GetHotelListByMatchingNameAsync_ReturnsFiveMatchingHotels(string name, string nonMatch)
{

    _hotelRepositoryMock = new Mock<IHotelRepository>();
    _hotelRepository = _hotelRepositoryMock.Object;

    // Set up sample data.
    var data = new List<Hotel>
    {
        new Hotel{Id = 1, Name = $"{name}", Description = "Description2", Location = "Location2", Rating = Rating.Two},
        new Hotel{Id = 2, Name = $"{name.ToUpper()}", Description = "Description1", Location = "Location1", Rating = Rating.Five},
        new Hotel{Id = 3, Name = $"{name.ToLower()}", Description = "Description2", Location = "Location2", Rating = Rating.Three},
        new Hotel{Id = 4, Name = $"{name} {nonMatch}", Description = "Description2", Location = "Location2", Rating = Rating.One},
        new Hotel{Id = 5, Name = nonMatch, Description = "Description2", Location = "Location2", Rating = Rating.One},
    };

    // Set up mock methods and ensure these method returns any sample data.
    _hotelRepositoryMock.Setup(x => x.GetListByMatchAsync(It.IsAny<string>()));
    _hotelRepositoryMock.Setup(x => x.GetAllAsync()).ReturnsAsync(data);


    var result = await _hotelRepository.GetListByMatchAsync(name);

    // Cast to list to make assertions.
    var hotels = result.ToList();

    Assert.That(hotels, Is.TypeOf<List<Hotel>>());
    Assert.That(hotels.Count, Is.EqualTo(4));
}

How can I make this test work such that the GetListByMatchAsync mock method does some logic after calling the mocked GetAllAsync method?

Answer 1

First, the code that you have shown cannot possibly work because the methods that you are trying to set up are not virtual. Declare the methods you want to Setup as virtual .

Second, this is wrong:

 _hotelRepositoryMock.Setup(x => x.GetListByMatchAsync(It.IsAny<string>())); 

With this call, you're effectively setting up GetListByMatchAsync to return default(Task<IEnumerable<Hotel>>) , ie null . That's obviously not what you want. Either:

• use .Returns(...) to specify what the method should return; or,
• use .CallBase() if the method should simply return whatever the implementation in the base class would return. (This is likely what you need.)