code: def test_astype_bytes(self):
      # GH#39474
      result = DataFrame(["foo", "bar", "baz"]).astype(bytes)
      assert result.dtypes[0] == np.dtype("S3")
  
imports: import re
  import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import Categorical, CategoricalDtype, DataFrame, DatetimeTZDtype, Index, Interval, IntervalDtype, NaT, Series, Timedelta, Timestamp, concat, date_range, option_context
  import pandas._testing
label_desc: Use image node_id 38 for calling the TestAstype obj's underlying member method code with example usage: obj.test_astype_bytes() without return types