public async Task DownloadBookSuccess()
{
//Arrange
var mockStream = new Mock <Stream>();
var fileServiceMock = new Mock <IBookService>();
fileServiceMock.Setup(m => m.GetBookForUserAsync(It.IsAny <string>(), It.IsAny <int>()))
.Returns(Task.FromResult(new Book()
{
Id = 1
}));
fileServiceMock.Setup(m => m.DownloadBookAsync(It.IsAny <string>(), It.IsAny <int>(), It.IsAny <string>()))
.Returns(Task.FromResult(mockStream.Object));
var storageMock = new Mock <IStorageService>();
var fileController = new BookController(_mapper, fileServiceMock.Object, _logger, storageMock.Object);
//Act
IActionResult actionResult = await fileController.DownloadBook("ID1", 1);
actionResult.ShouldNotBeNull();
OkObjectResult result = actionResult as OkObjectResult;
result.ShouldNotBeNull();
}