    def test_data_collection_flatten(self):
        """
        target: test flatten() API for DataCollection 
        method: create a data collection and flatten it
        expected: return flatten successfully
        """
        data = 10
        dc = DataCollection.range(data)
        size = 3
        res = dc.batch(size)
        result = res.flatten().to_list()
        assert len(result) == data

        return True
target: test flatten() API for DataCollection
method: create a data collection and flatten it
expected: return flatten successfully
tests/testcases/test_data_collection.py