total rows updated by sql query

Considering standalone editor with keyless data. If I want to use something like

$db
->query( 'update' )
->table( 'table_name' )
->set( 'test', $_POST['data']['keyless']['test'] )
->where( 'id', 1, '=' )
->exec();

How do I get the outcome of this query i.e. (Result) e.g. number of rows effected
I spent a lot of time looking for examples and reading the documentation without any luck.