[FIX] apropriate method calls, import tests

account_mass_reconcile_transaction_ref/models/base_advanced_reconciliation.py

@@ -1,16 +1,17 @@
 # Copyright 2013-2018 Camptocamp SA
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html)
-from odoo import models
+from odoo import models, api
 
 
 class MassReconcileAdvanced(models.AbstractModel):
 
     _inherit = 'mass.reconcile.advanced'
 
+    @api.model
     def _base_columns(self):
         """ Mandatory columns for move lines queries
         An extra column aliased as ``key`` should be defined
         in each query."""
-        aml_cols = super(MassReconcileAdvanced, self)._base_columns()
+        aml_cols = super()._base_columns()
         aml_cols.append('account_move_line.transaction_ref')
         return aml_cols