What can I do for model testing in Unit/Test on ruby

For model testing in Unit/test on ruby, I just test the DB saving of
all the tables?
Like this model
def self.get_latest_answers_for_person(person_id, limit=10)
return nil if person_id.nil?
return Answer.find_by_sql([’
SELECT * FROM answers
WHERE person_id = ?
ORDER BY created_at DESC
', person_id, limit])
I just test data in answer and users tables saving?