MAGETWO-58265: [Github][Cloud][Customer]Fix Varnish X-Header

- CR fixes

Author: Andrey Konosov

app/code/Magento/CacheInvalidate/Observer/InvalidateVarnishObserver.php

@@ -73,6 +73,6 @@ public function execute(\Magento\Framework\Event\Observer $observer)
      */
     private function getTagResolver()
     {
-        return ObjectManager::getInstance()->get('\Magento\Framework\App\Cache\Tag\Resolver');
+        return ObjectManager::getInstance()->get(\Magento\Framework\App\Cache\Tag\Resolver::class);
     }
 }

app/code/Magento/PageCache/Observer/FlushCacheByTags.php

@@ -74,10 +74,10 @@ private function getCache()
 
     /**
      * @deprecated
-     * @return \Magento\PageCache\Model\Cache\Tag\Resolver
+     * @return \Magento\Framework\App\Cache\Tag\Resolver
      */
     private function getTagResolver()
     {
-        return ObjectManager::getInstance()->get('\Magento\PageCache\Model\Cache\Tag\Resolver');
+        return ObjectManager::getInstance()->get(\Magento\Framework\App\Cache\Tag\Resolver::class);
     }
 }

lib/internal/Magento/Framework/App/Cache/Tag/Strategy/Dummy.php

@@ -17,6 +17,10 @@ class Dummy implements StrategyInterface
      */
     public function getTags($object)
     {
+        if (!is_object($object)) {
+            throw new \InvalidArgumentException('Provided argument is not an object');
+        }
+
         return [];
     }
 }

lib/internal/Magento/Framework/App/Cache/Tag/Strategy/Factory.php

@@ -48,7 +48,7 @@ public function __construct(
      *
      * @param object $object
      * @throws \InvalidArgumentException
-     * @return \Magento\Framework\App\Cache\Tag\StrategyInterface|null
+     * @return \Magento\Framework\App\Cache\Tag\StrategyInterface
      */
     public function getStrategy($object)
     {
@@ -62,7 +62,8 @@ class_parents($object),
             class_implements($object)
         );
 
-        if ($result = array_intersect(array_keys($this->customStrategies), $classHierarchy)) {
+        $result = array_intersect(array_keys($this->customStrategies), $classHierarchy);
+        if ($result) {
             return $this->customStrategies[array_shift($result)];
         }
 

lib/internal/Magento/Framework/App/Test/Unit/Cache/Tag/Strategy/DummyTest.php

@@ -10,16 +10,27 @@
 
 class DummyTest extends \PHPUnit_Framework_TestCase
 {
-    public function testGetTags()
+
+    private $model;
+
+    protected function setUp()
     {
-        $model = new Dummy();
-        $emptyArray = [];
+        $this->model = new Dummy();
+    }
 
-        $this->assertEquals($emptyArray, $model->getTags('scalar'));
+    public function testGetTagsWithScalar()
+    {
+        $this->setExpectedException(\InvalidArgumentException::class, 'Provided argument is not an object');
+        $this->model->getTags('scalar');
+    }
+
+    public function testGetTagsWithObject()
+    {
+        $emptyArray = [];
 
-        $this->assertEquals($emptyArray, $model->getTags(new \StdClass));
+        $this->assertEquals($emptyArray, $this->model->getTags(new \StdClass));
 
         $identityInterface = $this->getMockForAbstractClass(\Magento\Framework\DataObject\IdentityInterface::class);
-        $this->assertEquals($emptyArray, $model->getTags($identityInterface));
+        $this->assertEquals($emptyArray, $this->model->getTags($identityInterface));
     }
 }