Start writing unit tests

config/services.yml

@@ -7,8 +7,10 @@ services:
         alias: Pcm\IconBundle\Twig\Functions\IconExtension
         public: true
 
+
     Pcm\IconBundle\Twig\Functions\IconExtension:
+        tags: ['twig.extension']
         public: false
         arguments:
-            # $dir:
-                # - '%kernel.project_dir%/public/icons'
+            $directories:
+                - '%kernel.project_dir%/public/icons'