public async Task GetByIdAsync_ShouldReturnNotFoundResponseGivenTheIdDoesNotMatchAnAdvertisement() { var nonExistentId = new Fixture().Create <int>(); _advertisementService.Setup(x => x.GetByIdAsync(nonExistentId)).ReturnsAsync((Advertisement)null); var result = await _controller.GetByIdAsync(nonExistentId); result.Should().BeOfType <NotFoundResult>(); }