self = 
project_id = 'precise-truck-742'
def test_array_length_zero(self, project_id):
    query = """WITH t as (
               SELECT "a" letter, [""] as array_field
               UNION ALL
               SELECT "b" letter, [] as array_field)

               select letter, array_field, array_length(array_field) len
               from t
               order by letter ASC"""
    df = gbq.read_gbq(
        query,
        project_id=project_id,
        credentials=self.credentials,
        dialect="standard",
    )
    expected = DataFrame(
        [["a", [""], 1], ["b", [], 0]], columns=["letter", "array_field", "len"],
    )


  tm.assert_frame_equal(df, expected)


E       AssertionError: Attributes of DataFrame.iloc[:, 2] (column name="len") are different

E

E       Attribute "dtype" are different

E       [left]:  Int64

E       [right]: int64
tests/system/test_gbq.py:879: AssertionError