Add mock fetcher instead of real class using Carter framework

Question

Im doing integration testing on my rest web api. I have the following setup :

public ItemsControllerTests()
        {
            this.itemFetcher = new Mock<IItemFetcher>();
            this.itemFetcher.Setup(sp => sp.GetItems(It.IsAny<string>()))
            .Returns(Task.FromResult(
                (200, new Response<ICollection<Item>>()
                {
                    Data = new List<Item>()
                    {
                        new Item()
                        {
                            Id = 42,
                            Artwork = "http://cdn.fake.com/fake.png",
                            Category = new Category()
                            {
                                Id = 2,
                                Name = "musical"
                            },
                            Name = "Awesome bagpipe"
                        }
                    },
                    Error = null
                })
                ));
            client = new TestServer(new WebHostBuilder()
                    .ConfigureServices(services =>
                    {
                        //Middlewares
                        services.AddSingleton<IItemFetcher, ItemFetcher>();

                        services.AddCarter();
                    })
                    .Configure(app => { app.UseCarter(); })
                ).CreateClient();
        }

        [Fact]
        public async void GetItemsOK()
        {
            response = client.GetAsync("/items").GetAwaiter().GetResult();
            var content = await response.Content.ReadAsStringAsync();

            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
        }
    }

which works perfectly fine. the problem is its actually doing a REAL request as its using the real class. So my doubt is in this line :

services.AddSingleton<IItemFetcher, ItemFetcher>();

How can I use my mock object this.itemFetcher = new Mock(); instead of the real one. If I try this :

services.AddSingleton<IItemFetcher, itemFetcher>();

It fails as I am actually using an instance of a class instead of a class.

How can I overcome this?

Answer 1

ok. got it. You simply do it like this :

services.AddSingleton(itemFetcher);