ASP.Net Core unit testing async controller [duplicate]

Question

This question already has an answer here:

• How to mock an async repository with Entity Framework Core 4 answers

I have this test:

[Fact]
public async void Can_Paginate()
{
    //fake data
    var product1 = new Product { ProductId = 1, ProductName = "P1" };
    var product2 = new Product { ProductId = 2, ProductName = "Product 2" };
    var product3 = new Product { ProductId = 3, ProductName = "Product 3" };
    var product4 = new Product { ProductId = 4, ProductName = "Product 4" };
    var product5 = new Product { ProductId = 5, ProductName = "Product 5" };
    var data = new List<Product>
    {
         product1,
         product2,
         product3,
         product4,
         product5
     }.ToAsyncEnumerable();

      var category1 = new Category { CategoryId = 1 };

      var prodCategoryData = new List<ProductCategory>
      {
          new ProductCategory { Product =product1,Category = category1},
          new ProductCategory { Product =product2,Category = category1},
          new ProductCategory { Product =product3,Category = category1},
          new ProductCategory { Product =product4,Category = category1},
          new ProductCategory { Product =product5,Category = category1}
      }.ToAsyncEnumerable();

      var dbSetMock = new Mock<DbSet<Product>>();
      //dbSetMock.As<IQueryable<Product>>().Setup(m => m.Provider).Returns(data.Provider);
      //dbSetMock.As<IQueryable<Product>>().Setup(m => m.Expression).Returns(data.Expression);
      //dbSetMock.As<IQueryable<Product>>().Setup(m => m.ElementType).Returns(data.ElementType);
      //dbSetMock.As<IQueryable<Product>>().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());

      var pcDbSetMock = new Mock<DbSet<ProductCategory>>();
      // pcDbSetMock.As<IQueryable<ProductCategory>>().Setup(m => m.Provider).Returns(prodCategoryData.Provider);
      //pcDbSetMock.As<IQueryable<ProductCategory>>().Setup(m => m.Expression).Returns(prodCategoryData.Expression);
      //pcDbSetMock.As<IQueryable<ProductCategory>>().Setup(m => m.ElementType).Returns(prodCategoryData.ElementType);
      //pcDbSetMock.As<IQueryable<ProductCategory>>().Setup(m => m.GetEnumerator()).Returns(prodCategoryData.GetEnumerator());

      Mock<ApplicationDbContext> customDbContextMock = new Mock<ApplicationDbContext>();
      customDbContextMock.Setup(x => x.Products).Returns(dbSetMock.Object);
      customDbContextMock.Setup(x => x.ProductCategories).Returns(pcDbSetMock.Object);

      var loggerMock = new Mock<ILogger<ProductsController>>();
      var envMock = new Mock<IHostingEnvironment>();
      var httpContext = new Mock<HttpContext>().Object;
      var actionDescriptor = new Mock<Microsoft.AspNetCore.Mvc.Controllers.ControllerActionDescriptor>().Object;
      var modelState = new ModelStateDictionary();
      var actionContext = new ActionContext(httpContext, new Mock<RouteData>().Object, actionDescriptor, modelState);

      ProductsController controller = new ProductsController(customDbContextMock.Object, loggerMock.Object, envMock.Object);
      controller.pageSize = 3;
      controller.ControllerContext = new ControllerContext(actionContext);
      var result = await controller.List(1, 2);

My controller logic:

public async Task<IActionResult> List(int Id, int page = 1)
{

   if (Id == 0)
   {
       ViewBag.CategoryName = "Wszystkie produkty";
       return View(await _context.ProductCategories.Include(c => c.Product).ToListAsync());
   }

   return View(await _context.ProductCategories
       .Include(p => p.Product)
       .Where(pt => pt.CategoryId == Id)
       .OrderBy(p=>p.ProductId)
       .Skip((page-1)*pageSize)
       .ToListAsync());
}

My problem is that I cannot mock _context.ProductCategories by using prodCategoryData and data lists as IAsyncEnumerable.

When I cast them to IQueryable I get this error instead:

Additional information: The source IQueryable doesn't implement IAsyncEnumerable<WineCom.Models.ProductCategory>. Only sources that implement IAsyncEnumerable can be used for Entity Framework .

Answer 1

Using the test classes from this answer :

How to mock an async repository with Entity Framework Core

The following generic extension method was derived

public static Mock<DbSet<T>> ToAsyncDbSetMock<T>(this IEnumerable<T> source)
    where T : class {

    var data = source.AsQueryable();

    var mockSet = new Mock<DbSet<T>>();

    mockSet.As<IAsyncEnumerable<T>>()
        .Setup(m => m.GetEnumerator())
        .Returns(new TestAsyncEnumerator<T>(data.GetEnumerator()));

    mockSet.As<IQueryable<T>>()
        .Setup(m => m.Provider)
        .Returns(new TestAsyncQueryProvider<T>(data.Provider));

    mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(data.Expression);
    mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(data.ElementType);
    mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(() => data.GetEnumerator());

    return mockSet;
}

With the above extension method the test can be refactored to

[Fact]
public async Task Can_Paginate() {

    //Arrange

    var products = GetFakeProducts().ToAsyncDbSetMock();    
    var productCategories = GetFakeProductCategories().ToAsyncDbSetMock();

    var customDbContextMock = new Mock<ApplicationDbContext>();
    customDbContextMock.Setup(x => x.Products).Returns(products.Object);
    customDbContextMock.Setup(x => x.ProductCategories).Returns(productCategories.Object);

    //...other code removed for brevity

    var controller = new ProductsController(customDbContextMock.Object, loggerMock.Object, envMock.Object);
    controller.pageSize = 3;
    controller.ControllerContext = new ControllerContext(actionContext);

    //Act
    var result = await controller.List(1, 2);

    //Assert

    //...other code removed for brevity
}