Dumplie\Customer\Domain\Cart::add PHP Method

    public function add(Product $product, int $quantity)
    {
        if (!$product->isAvailable()) {
            throw new ProductNotAvailableException($product);
        }
        if (!$product->price()->hasCurrency($this->currency)) {
            throw new InvalidCurrencyException($this->currency, $product->price()->currency());
        }
        if (array_key_exists((string) $product->sku(), $this->items)) {
            $quantity += $this->items[(string) $product->sku()]->quantity();
        }
        $this->items[(string) $product->sku()] = new CartItem($product->sku(), $quantity);
    }

 function it_can_be_used_to_place_order(Products $products, Carts $carts)
 {
     $product = new Product(new SKU("SKU"), Price::EUR(1000), true);
     $cart = new Cart(CartId::generate(), 'EUR');
     $cart->add($product, 1);
     $carts->getById(Argument::type(CartId::class))->willReturn($cart);
     $products->getBySku(Argument::type(SKU::class))->willReturn($product);
     $order = $this->placeOrder(OrderId::generate(), $products, $carts);
     $order->shouldBeAnInstanceOf(Order::class);
 }