feat(Filter): add method to create a subtree filter with an array of IDs

Closes #257

src/Model/Product/Search/FilterSubtreeCollection.php

@@ -6,6 +6,7 @@
 namespace Commercetools\Core\Model\Product\Search;
 
 use Commercetools\Core\Model\Common\Collection;
+use Commercetools\Core\Model\Common\Context;
 
 /**
  * @package Commercetools\Core\Model\Product\Search
@@ -26,4 +27,20 @@ public function __toString()
         }
         return implode(',', $values);
     }
+
+    /**
+     * @param array $ids
+     * @param Context|null $context
+     * @return FilterSubtreeCollection
+     */
+    public static function ofIds(array $ids, Context $context = null)
+    {
+        $collection = static::of($context);
+
+        foreach ($ids as $id) {
+            $collection->add(FilterSubtree::ofId($id));
+        }
+
+        return $collection;
+    }
 }

tests/unit/Model/Product/Search/FilterSubtreeTest.php

@@ -23,6 +23,12 @@ public function testDefaultType()
         $this->assertSame('subtree("12345"),subtree("abcde")', (string)$subtrees);
     }
 
+    public function testCollectionIds()
+    {
+        $subtrees = FilterSubtreeCollection::ofIds(['12345', 'abcde']);
+        $this->assertSame('subtree("12345"),subtree("abcde")', (string)$subtrees);
+    }
+
     public function testIntValue()
     {
         $subtree = FilterSubtree::ofId(12345);