FakeItEasy ControllerTest HttpGet Calls - testing

Question

I want to start using FakeItEasy for testing queries.
The tests I want to write should check if entities are returned on HttpGet calls (get all and get by Id)
The Controller:
public class ToDoController : ControllerBase
{
private readonly IMediator _mediator;
public ToDoController(IMediator mediator) =>
_mediator = mediator;
[HttpGet]
[Produces("application/json")]
[ProducesResponseType(typeof(IEnumerable<ToDoItem>), (int)HttpStatusCode.OK)]
public async Task<ActionResult<IEnumerable<ToDoItem>>> Get()
{
var result = await _mediator.Send(new ToDoItemsQuery(new
AllToDoItems())).ConfigureAwait(false);
if (result != null && result.Any())
{
return result.ToList();
}
throw new InvalidOperationException("TODO: error handling");
}
[HttpGet]
[Route("{id}")]
[Produces("application/json")]
[ProducesResponseType(typeof(ToDoItem), (int)HttpStatusCode.OK)]
public async Task<ActionResult<ToDoItem>> GetById(int itemId)
{
var result = await _mediator
.Send(new ToDoItemsQuery(new ToDoItemById(itemId)))
.ConfigureAwait(false);
if (result != null && result.Any())
{
return result.FirstOrDefault();
}
throw new InvalidOperationException("TODO: error handling");
}
}
}
The TestClass:
public class ToDoItemControllerTests : ControllerTestBase
{
private IMediator _mediator;
private ToDoController _sut;
public ToDoItemControllerTests()
{
_mediator = A.Fake<IMediator>();
_sut = new ToDoController(_mediator);
}
[TestMethod]
public async Task GetAllItemsAsync_SuccessTest()
{
A.CallTo(() => _mediator.Send(A<AllToDoItems>._,
A<CancellationToken>._)).Returns(A.CollectionOfFake<ToDoItem>(10));
var result = await _sut.Get();
Assert.IsNotNull(result);
A.CallTo(() => _mediator).MustHaveHappened();
}
[TestMethod]
public async Task GetItemByIdAsync_SuccessTest()
{
// Arrange
int itemId = 2;
var commandResult =
new List<ToDoItem>
{
new ToDoItem
{
Id = itemId
};
}
A.CallTo(() => MediatR.Send(A<ToDoItemById>._, A<CancellationToken>._)).Returns(commandResult);
// Act
var result = await _sut.GetById(itemId);
// Assert
Assert.IsNotNull(result);
A.CallTo(() => MediatR.Send(A<ToDoItemById>._, A<CancellationToken>._)).MustHaveHappened();
}
}
So in the first test I set up A.CallTo the interface IMediatR to return 10 ToDoItems.
During debug I see the _sut.Get() enter the controller, entering the correct method/api call.
The _mediator.Send() in the controller returns a Fake IEnumerable (not the 10 items i set up in the first Call.To in the testmethod, but an enumeration that yields no results).
Because of the result.Any() being false, the controller throws an InvalidOperationException
And I cannot even Assert the result.IsNotNull()
The second test I want to Test If 1 item is returned upon calling the API.
I set up (a) an itemId of type int for parameter,
(b) A mocked(?) List with 1 Item from the setup with the itemId and
(c) a call to the mediatR should return the mocked Listfrom (b)
I make the call from the test, in debug I see the call await _mediator.Sent() returning
A Fake Ienumerable of ToDoItem, result is not null, but because result.Any() is false,
the item doesn't get returned, and I get another InvalidOperationException
I feel like I'm missing something in the setup of the tests..
A Fake database Interface?
I don't want to chance my controller and make the if less restrictive, just so my test would pass
EDIT:
Even if I change the if condition to removing the Any condition
and I see the test entering the controller, returning "First Or Default" of the result,
The test fails on A Call To Must Have Happened.
Expected to find it once or more but no calls were made to the fake object.
This I really don't get, i actually see him making the call?!
I've browsed GitHub to find examples but the closest I found was Entities with methods, with those methods being defined in an interface. This is not the case here
Seeing as the official documentation doesn't make me any wiser I turn to SO <3
Thanks in advance!

Answer 1

In the first test, you configure the call to Send with an argument of type AllToDoItems. But in the controller, you actually call Send with a TodoItemsQuery. So the call doesn't match, and the default (unconfigured) behavior, which is to return a fake IEnumerable, applies. You need to configure the call like this:
A.CallTo(() => _mediator.Send(A<TodoItemsQuery>._,
A<CancellationToken>._)).Returns(A.CollectionOfFake<ToDoItem>(10));
In the second test, the problem is the same, with ToDoItemById instead of AllToDoItems