[impr-OpenMage#883] Add test method to cache models and fix layout up…

…date test

app/code/core/Mage/Core/Model/App.php

@@ -1183,6 +1183,17 @@ public function saveCache($data, $id, $tags=array(), $lifeTime=false)
         return $this;
     }
 
+    /**
+     * Test cache record availability
+     *
+     * @param   string $id
+     * @return  false|int
+     */
+    public function testCache($id)
+    {
+        return $this->_cache->test($id);
+    }
+
     /**
      * Remove cache
      *

app/code/core/Mage/Core/Model/Cache.php

@@ -403,6 +403,17 @@ public function save($data, $id, $tags = array(), $lifeTime = null)
         return $this->getFrontend()->save((string)$data, $this->_id($id), $this->_tags($tags), $lifeTime);
     }
 
+    /**
+     * Test data
+     *
+     * @param string $id
+     * @return false|int
+     */
+    public function test($id)
+    {
+        return $this->getFrontend()->test($this->_id($id));
+    }
+
     /**
      * Remove cached data by identifier
      *

app/code/core/Mage/Core/Model/Layout/Update.php

@@ -213,7 +213,7 @@ public function saveCache()
         Mage::app()->saveCache($hash, $this->getCacheId(), $tags, null);
 
         // Only save actual XML to cache if it doesn't already exist
-        if ( ! Mage::app()->getCache()->test(self::XML_KEY_PREFIX . $hash)) {
+        if ( ! Mage::app()->testCache(self::XML_KEY_PREFIX . $hash)) {
             Mage::app()->saveCache($str, self::XML_KEY_PREFIX . $hash, $tags, null);
         }
         return TRUE;