Symfony arrays from actions turn into sfOutputEscaperArrayDecorator objects in template.

In symfony a common problem is that arrays that are passed on from the action to the template are turned into sfOutputEscaperArrayDecorator. Then functions like is_array($testArray) won't work anymore.

this->testArray = array('1'=>'a', '2'=>'b', '3'=>'c');

Turning output escaping off

This happens when you have output escaping enabled in Symfony.
If you don't need it you can turn it off in:

myapp/apps/frontend/config/settings.yml

Find the entry and set it to false.

all:
   escaping_strategy:    false

Solution with keeping output escaping enabled

In the action.class.php:

this->testArray = array('1'=>'a', '2'=>'b', '3'=>'c');

In the template.php:

$myArray = $sf_data->getRaw('testArray');