public void SubtractQuantity_Should_DecreaseQuantity(int value)
{
var shoppingCartPosition = new ShoppingCartPosition <Book>(_book, 10);
shoppingCartPosition.SubtractQuantity(value);
var expected = shoppingCartPosition.Quantity -= value;
shoppingCartPosition.Quantity.Should().Be(expected);
}
public void SubtractQuantity_For_Negative_Throw_NegativeQuantity(int value)
{
FluentActions.Invoking(() => _shoppingCartPosition.SubtractQuantity(value))
.Should()
.Throw <NegativeQuantity>();
}