Fix using tables in fixtures that don't have entity configs.

app/code/community/EcomDev/PHPUnit/Model/Mysql4/Fixture.php

@@ -27,6 +27,7 @@ class EcomDev_PHPUnit_Model_Mysql4_Fixture extends Mage_Core_Model_Mysql4_Abstra
     protected function _construct()
     {
         $this->_setResource('ecomdev_phpunit');
+        $this->_resourceModel = NULL;
     }
 
     /**
@@ -131,4 +132,4 @@ class EcomDev_PHPUnit_Model_Mysql4_Fixture extends Mage_Core_Model_Mysql4_Abstra
 
         throw new InvalidArgumentException('Unrecognized type for DB column');
     }
-}
\ No newline at end of file
+}