ShipProduct.cs

public void ShipProduct(int quantity)
{
    // Trivial Validation
    if (quantity <= 0)
    {
        throw new InvalidDomainException("Quantity must be greater than zero.");
    }

    // Business Rule
    if (quantity > _warehouseProductState.QuantityOnHand)
    {
        throw new InvalidDomainException("Cannot Ship to a negative Quantity on Hand.");
    }

    var productShipped = new ProductShipped(Sku, quantity, DateTime.UtcNow);

    Apply(productShipped);
    Add(productShipped);
}