[FIX] the result of the binding is not always None but also False. Indeed in Magento for exemple we use a read for returning the binding and OpenERP/Odoo return False if the binding value is empty
[IMP] improve common test, give the posibility to return a callable for mocking Magento Call. Indeed we do not want that the mock return always the same magento id. Take a look into magentoerpconnect_catalog for more information