def test_auto_increment_must_increment_id_of_new_documents(db):
c = db.collection1
c.insert({'_id':20})
save_doc_with_autoincremented_id(c, {'field':'value'})
assert c.find_one({'_id':21})['field'] == 'value'
def test_auto_increment_on_concurent_document_saves(db):
c = db.collection1
c.insert({'_id':20})
def insert():
c.save({'_id':21})
save_doc_with_autoincremented_id(c, {'field':'value'}, insert)
assert c.find_one({'_id':22})['field'] == 'value'
def test_auto_increment_must_not_change_id_of_existing_documents(db):
c = db.collection1
c.insert({'_id':20})
doc = c.find_one({'_id':20})
doc['field'] = 'value'
save_doc_with_autoincremented_id(c, doc)
assert c.find_one({'_id':20})['field'] == 'value'
assert not c.find({'_id':21}).count()
