code: def test_does_not_convert_mixed_integer(self):
      df = DataFrame(
          np.ones((3, 2)), columns=date_range("2020-01-01", periods=2)
      )
      cols = df.columns.join(df.index, how="outer")
      joined = cols.join(df.columns)
      assert cols.dtype == np.dtype("O")
      assert cols.dtype == joined.dtype
      tm.assert_numpy_array_equal(cols.values, joined.values)
  
file_path: pandas/pandas/tests/indexes/datetimes/test_join.py
imports: from datetime import datetime, timezone
  import numpy
  import pytest
  from pandas import DataFrame, DatetimeIndex, Index, Timestamp, date_range, period_range, to_datetime
  import pandas._testing
  from pandas.tseries.offsets import BDay, BMonthEnd
label_desc: Use image node_id 1 for calling the TestJoin obj's underlying member method code with example usage: obj.test_does_not_convert_mixed_integer() without return types