XUnit + Moq + FluentAssertions, checking for null on Task instead of proper object

Question

I am new to unit testing and moq.

Using Postman to test DeleteItemAsync(),

    [HttpDelete("{id:length(24)}")]
    public async Task<IActionResult> DeleteItemAsync(string id)
    {
        var item = _ItemRepo.GetItemByIdAsync(id);
        if (item == null)
            return NotFound();
        await _itemRepo.DeleteItemAsync(id);
        return NoContent();
    }

when the item isn't found, I get the proper result, NotFound.

When running my unit test it's failing because, in the controller, it is checking for null on the Task object returned by the moq _repoStub call to GetItemByIdAsync(id).

    [Fact]
    public async Task DeleteItemAsync_ItemDoesntExist_ReturnsNotFound()
    {
        // Arrange
        _repoStub
            .Setup(repo => repo.GetItemByIdAsync(It.IsAny<String>()))
            .ReturnsAsync((Item)null);
        _repoStub
            .SetupSequence(repo => repo.DeleteItemAsync(It.IsAny<String>()))
            .Returns(Task.FromResult<NotFoundResult>(null));

        var controller = new ItemController(_repoStub.Object, _mapperStub);

        // Act
        var actionResult = await controller.DeleteItemAsync(It.IsAny<String>());

        // Assert
        actionResult.Should().BeOfType<NotFoundResult>();
    }

Answer 1

GetItemByIdAsync should be awaited in the subject under test

[HttpDelete("{id:length(24)}")]
public async Task<IActionResult> DeleteItemAsync(string id)
{
    var item =  await _ItemRepo.GetItemByIdAsync(id); //<--!!!
    if (item == null)
        return NotFound();
    await _itemRepo.DeleteItemAsync(id);
    return NoContent();
}

otherwise it will return a Task and thus not be null as shown by your error.

Also, note that It.IsAny should only be used in expectation expressions and not as a variable

[Fact]
public async Task DeleteItemAsync_ItemDoesntExist_ReturnsNotFound()
{
    // Arrange
    _repoStub
        .Setup(repo => repo.GetItemByIdAsync(It.IsAny<String>()))
        .ReturnsAsync((Item)null);
    _repoStub
        .SetupSequence(repo => repo.DeleteItemAsync(It.IsAny<String>()))
        .Returns(Task.FromResult<NotFoundResult>(null));

    var controller = new ItemController(_repoStub.Object, _mapperStub);

    // Act
    var actionResult = await controller.DeleteItemAsync(""); //<--It.IsAny<String>() removed

    // Assert
    actionResult.Should().BeOfType<NotFoundResult>();
}