MAGETWO-83872: Write metadata service

Author: Eric Bohanon

dev/tests/api-functional/testsuite/Magento/Downloadable/Api/ProductRepositoryTest.php

@@ -605,6 +605,15 @@ protected function deleteProductBySku($productSku)
      */
     protected function saveProduct($product)
     {
+        if (isset($product['custom_attributes'])) {
+            for ($i=0; $i<sizeof($product['custom_attributes']); $i++) {
+                if ($product['custom_attributes'][$i]['attribute_code'] == 'category_ids'
+                    && !is_array($product['custom_attributes'][$i]['value'])
+                ) {
+                    $product['custom_attributes'][$i]['value'] = [""];
+                }
+            }
+        }
         $resourcePath = self::RESOURCE_PATH . '/' . $product['sku'];
         $serviceInfo = [
             'rest' => [