Added the wrapper for creating shell instances.

src/Console/CommandRunner.php

@@ -155,7 +155,7 @@ public function run(array $argv, ConsoleIo $io = null)
     /**
      * Get the shell instance for a given command name
      *
-     * @param \Cake\Console\ConsoleIo $io The io wrapper for the created shell class.
+     * @param \Cake\Console\ConsoleIo $io The IO wrapper for the created shell class.
      * @param \Cake\Console\CommandCollection $commands The command collection to find the shell in.
      * @param string $name The command name to find
      * @return \Cake\Console\Shell
@@ -173,7 +173,7 @@ protected function getShell(ConsoleIo $io, CommandCollection $commands, $name)
         }
         $instance = $commands->get($name);
         if (is_string($instance)) {
-            $instance = new $instance($io);
+            $instance = $this->createShell($instance, $io);
         }
         $instance->setRootName($this->root);
         if ($instance instanceof CommandCollectionAwareInterface) {
@@ -182,4 +182,16 @@ protected function getShell(ConsoleIo $io, CommandCollection $commands, $name)
 
         return $instance;
     }
+
+    /**
+     * The wrapper for creating shell instances.
+     *
+     * @param string $className Shell class name.
+     * @param \Cake\Console\ConsoleIo $io The IO wrapper for the created shell class.
+     * @return \Cake\Console\Shell
+     */
+    protected function createShell($className, ConsoleIo $io)
+    {
+        return new $className($io);
+    }
 }