code: def test_lower_upper_mixed_object():
      s = Series(
          [
              "a",
              np.nan,
              "b",
              True,
              datetime.today(),
              "foo",
              None,
              1,
              2.0,
          ]
      )
  
      result = s.str.upper()
      expected = Series(
          [
              "A",
              np.nan,
              "B",
              np.nan,
              np.nan,
              "FOO",
              None,
              np.nan,
              np.nan,
          ],
          dtype=object,
      )
      tm.assert_series_equal(result, expected)
  
      result = s.str.lower()
      expected = Series(
          [
              "a",
              np.nan,
              "b",
              np.nan,
              np.nan,
              "foo",
              None,
              np.nan,
              np.nan,
          ],
          dtype=object,
      )
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime
  import operator
  import numpy
  import pytest
  from pandas import Series, _testing
label_desc: Use image node_id 4 for calling a global function with example usage: test_lower_upper_mixed_object() without return types