client_and_types = (, )
project_id = 'precise-truck-742'
table_with_data_ref = 'projects/precise-truck-742/datasets/bq_storage_system_tests_42335d05_507f_48e0_8c32_033823270111/tables/users'
bq_client = 
def test_snapshot(client_and_types, project_id, table_with_data_ref, bq_client):
    client, types = client_and_types
    before_new_data = dt.datetime.now(tz=dt.timezone.utc)

    # load additional data into the table
    new_data = [
        {"first_name": "NewGuyFoo", "last_name": "Smith", "age": 46},
        {"first_name": "NewGuyBar", "last_name": "Jones", "age": 30},
    ]

    destination = _to_bq_table_ref(table_with_data_ref)
    bq_client.load_table_from_json(new_data, destination).result()

    # read data using the timestamp before the additional data load

    read_session = types.ReadSession()
    read_session.table = table_with_data_ref
    read_session.table_modifiers.snapshot_time = before_new_data
    read_session.data_format = types.DataFormat.AVRO

    session = client.create_read_session(
        request={
            "parent": "projects/{}".format(project_id),
            "read_session": read_session,
            "max_stream_count": 1,
        }
    )
    stream = session.streams[0].name

    rows = list(client.read_rows(stream).rows(session))

    # verify that only the data before the timestamp was returned


  assert len(rows) == 5  # all initial records


E       assert 0 == 5

E        +  where 0 = len([])
tests/system/reader/test_reader.py:212: AssertionError