public async Task DeleteAuthor_WhenCallingValidRequest_ShouldReturnOk()
        {
            // Arrange
            _authorServiceMock.Setup(a =>
                                     a.DeleteAuthor(It.IsAny <Guid>()));

            // Act
            IActionResult actionResult = await _authorsApiController
                                         .DeleteAuthor(new Guid());

            NoContentResult result = actionResult as NoContentResult; // null if cast fails

            // Assert
            Assert.IsNotNull(actionResult);
            Assert.IsNotNull(result);
        }