Implemented some new tests.

app/Repositories/PiggyBank/PiggyBankRepositoryInterface.php

@@ -42,6 +42,11 @@ interface PiggyBankRepositoryInterface
      */
     public function getEvents(PiggyBank $piggyBank);
 
+    /**
+     * @return int
+     */
+    public function getMaxOrder();
+
     /**
      * @return Collection
      */