unit testing a webapi async action

Question

I am new to unit testing but trying to get my head around it to try improve the quality of code I write.

I have created a webapi2 project that returns a customer like

   public async Task<IHttpActionResult> GetCustomer([FromUri]int id)
    {
         var customer = await _repository.FindCustomerAsync(id);
         return Ok(customer);
    }

My repository

 public async Task<Customer> FindCustomerAsync(int id)
    {
        using (var context = new MyContext())
        {
            var result = await context.Customers.FindAsync(id);
            return result;    
        }

    }

Previously I was not returning an async task at it was very easy to test. Migrating the action to a async task has made it a little hard for me to test.

I am using Moq and Xunit and my attempt at a unit test looks like

 [Fact()]
    public async void GetCustomer()
    {
        var id = 2;

        _customerMock.Setup(x => x.FindCustomerAsync(id))
            .Returns(Task.FromResult(FakeCustomers()
            .SingleOrDefault(cust => cust.customerID == id)));


        var controller = new CustomersController(_customerMock.Object).GetCustomer(id);
        var result = await controller as Customer;

        Assert.NotNull(result);

        //Assert.IsType<OkNegotiatedContentResult<Customer>>(negotiatedResult);
        //Assert.Equal(negotiatedResult.Content.customerID, id);
    }

My FakeCustomers

  private IQueryable<Customer> FakeCustomers()
    {
        return new List<Customer>()
    {
        new Customer()
        {
            customerID = 1,
            firstName = "Brian",
            lastName = "Smith"
        },
        new Customer()
        {
            customerID = 2,
            firstName = "Tom",
        }
    }.AsQueryable();
    }

the test always fails when trying to cast to Customer {"Object reference not set to an instance of an object."}

What I am doing wrong with my test?

Answer 1

Can you try this way?:

[Fact()]
public async void GetCustomer()
{
    var id = 2;

    _customerMock.Setup(x => x.FindCustomerAsync(id))
        .Returns(Task.FromResult(new Customer()
                 {
                  customerID = 2,
                  firstName = "Tom",
                 }));


    var controller = new CustomersController(_customerMock.Object).GetCustomer(id);
    var result = await controller as Customer;

    Assert.NotNull(result);
}