[Api] Add validation to add to cart command

features/cart/shopping_cart/adding_product_to_cart.feature

@@ -25,3 +25,10 @@ Feature: Adding a simple product to the cart
         And I should be notified that the product has been successfully added
         And there should be one item in my cart
         And this item should have name "Oathkeeper"
+
+    @api
+    Scenario: Preventing adding to cart item with 0 quantity
+        Given the store has a product "T-shirt banana" priced at "$12.54"
+        When I try to add 0 products "T-shirt banana" to the cart
+        Then I should be notified that quantity of added product should be greater than 0
+        And there should be 0 item in my cart

src/Sylius/Behat/Context/Api/Shop/CartContext.php

@@ -109,6 +109,7 @@ public function iAddThisProductToTheCart(ProductInterface $product, string $toke
     /**
      * @When /^I add (\d+) of (them) to (?:the|my) (cart)$/
      * @When /^I add (\d+) (products "[^"]+") to the (cart)$/
+     * @When /^I try to add (\d+) (products "[^"]+") to the (cart)$/
      */
     public function iAddOfThemToMyCart(int $quantity, ProductInterface $product, string $tokenValue): void
     {
@@ -221,6 +222,18 @@ public function iShouldBeNotifiedThatTheProductHasBeenSuccessfullyAdded(): void
         );
     }
 
+    /**
+     * @Then I should be notified that quantity of added product should be greater than 0
+     */
+    public function iShouldBeNotifiedThatQuantityOfAddedProductShouldBeMoreThan0(): void
+    {
+        $response = $this->cartsClient->getLastResponse();
+        Assert::false(
+            $this->responseChecker->isUpdateSuccessful($response),
+            SprintfResponseEscaper::provideMessageWithEscapedResponseContent('Quantity of added item should by grater than 0', $response)
+        );
+    }
+
     /**
      * @Then there should be one item in my cart
      */
@@ -234,6 +247,17 @@ public function thereShouldBeOneItemInMyCart(): void
         $this->sharedStorage->set('item', $items[0]);
     }
 
+    /**
+     * @Then /^there should be (\d+) item in my (cart)$/
+     */
+    public function thereShouldCountItemsInMyCart(int $count, string $cartToken): void
+    {
+        $response = $this->cartsClient->show($cartToken);
+        $items = $this->responseChecker->getValue($response, 'items');
+
+        Assert::count($items, $count);
+    }
+
     /**
      * @Then /^(this item) should have name "([^"]+)"$/
      */

src/Sylius/Bundle/ApiBundle/Resources/config/validation/AddItemToCart.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+
+ This file is part of the Sylius package.
+
+ (c) Paweł Jędrzejewski
+
+ For the full copyright and license information, please view the LICENSE
+ file that was distributed with this source code.
+
+-->
+
+<constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/services/constraint-mapping-1.0.xsd">
+    <class name="Sylius\Bundle\ApiBundle\Command\Cart\AddItemToCart">
+        <property name="quantity">
+            <constraint name="NotNull" />
+            <constraint name="Positive">
+                <option name="message">sylius.cart_item.greater_than_0</option>
+                <option name="groups">
+                    <value>sylius</value>
+                </option>
+            </constraint>
+        </property>
+    </class>
+</constraint-mapping>

src/Sylius/Bundle/CoreBundle/Resources/translations/validators.en.yml

@@ -34,6 +34,7 @@ sylius:
             not_valid: The currency code you entered is invalid.
     cart_item:
         not_available: '%itemName% does not have sufficient stock.'
+        greater_than_0: 'Quantity of added item should by grater than 0'
     order:
         currency_code:
             not_valid: The currency code you entered is invalid.