rewrite interface and create first tests

Export/FilterInterface.php

@@ -19,19 +19,19 @@
 
 namespace Chill\MainBundle\Export;
 
-use Doctrine\ORM\QueryBuilder;
-use Symfony\Component\Form\FormBuilderInterface;
 
 /**
+ * Interface for filters. 
+ * 
+ * Filter will filter result on the query initiated by Export. Most of the time, 
+ * it will add a `WHERE` clause on this query.
+ * 
+ * Filters should not add column in `SELECT` clause.
  * 
  *
  * @author Julien Fastré <julien.fastre@champs-libres.coop>
  */
-interface FilterInterface extends ExportElementInterface
+interface FilterInterface extends ModifierInterface
 {
-    public function applyOn();
-    
-    public function buildForm(FormBuilderInterface $builder);
-    
-    public function alterQuery(QueryBuilder $qb, $data);
+
 }