code: def test_repr_should_return_str(self):
      # https://docs.python.org/3/reference/datamodel.html#object.__repr__
      # "...The return value must be a string object."
  
      # (str on py2.x, str (unicode) on py3)
  
      data = [8, 5, 3, 5]
      index1 = ["\u03c3", "\u03c4", "\u03c5", "\u03c6"]
      cols = ["\u03c8"]
      df = DataFrame(data, columns=cols, index=index1)
      assert type(df.__repr__()) is str  # noqa: E721
  
      ser = df[cols[0]]
      assert type(ser.__repr__()) is str
  
imports: from datetime import datetime, timedelta
  from io import StringIO
  import numpy
  import pytest
  from pandas._config import using_pyarrow_string_dtype
  from pandas import NA, Categorical, CategoricalIndex, DataFrame, IntervalIndex, MultiIndex, NaT, PeriodIndex, Series, Timestamp, date_range, option_context, period_range
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestDataFrameRepr obj's underlying member method code with example usage: obj.test_repr_should_return_str() without return types