public async Task PostAsyncWithValidationErrorsReturnsBadRequest()
{
// Arrange
var newBooking = new NewBookingViewModel()
{
PassengersName = "PersonName"
};
_controller.ModelState.AddModelError("FlightNumber", "The FlightNumber field is required.");
// Act
var result = await _controller.PostAsync(newBooking);
// Assert
Assert.IsType <BadRequestObjectResult>(result);
}