public async Task BuyProductPost_ReturnsBadRequestResult_WhenModelStateIsInvalid()
{
_controller.ModelState.AddModelError("TypeProduct", "Required");
var param = new CreatorProductDTO();
// Act
var response = await _controller.BuyProduct(param);
// Assert
var actionResult = Assert.IsType <ActionResult <ProductDTO> >(response);
Assert.IsType <BadRequestObjectResult>(actionResult.Result);
}