MAGETWO-33060: Refactor __() to return Phrase object

- Method getSpecifyOptionMessage returns Phrase object;

Author: Dmytro Poperechnyy

app/code/Magento/ConfigurableProduct/Model/Product/Type/Configurable.php

@@ -809,7 +809,7 @@ protected function _prepareProduct(\Magento\Framework\Object $buyRequest, $produ
             }
         }
 
-        return $this->getSpecifyOptionMessage();
+        return (string)$this->getSpecifyOptionMessage();
     }
 
     /**
@@ -834,7 +834,7 @@ public function checkProductBuyState($product)
                 }
             }
             if (empty($attributes)) {
-                throw new \Magento\Framework\Model\Exception($this->getSpecifyOptionMessage());
+                throw new \Magento\Framework\Model\Exception((string)$this->getSpecifyOptionMessage());
             }
         }
         return $this;
@@ -843,11 +843,11 @@ public function checkProductBuyState($product)
     /**
      * Retrieve message for specify option(s)
      *
-     * @return string
+     * @return \Magento\Framework\Phrase
      */
     public function getSpecifyOptionMessage()
     {
-        return (string)__('Please specify the product\'s option(s).');
+        return __('Please specify the product\'s option(s).');
     }
 
     /**

dev/tests/integration/testsuite/Magento/ConfigurableProduct/Model/Product/Type/ConfigurableTest.php

@@ -291,7 +291,10 @@ public function testPrepareForCart()
 
     public function testGetSpecifyOptionMessage()
     {
-        $this->assertEquals('Please specify the product\'s option(s).', $this->_model->getSpecifyOptionMessage());
+        $this->assertEquals(
+            'Please specify the product\'s option(s).',
+            (string)$this->_model->getSpecifyOptionMessage()
+        );
     }
 
     /**