code: def test_append_empty(self, float_frame):
      empty = DataFrame()
  
      appended = float_frame._append(empty)
      tm.assert_frame_equal(float_frame, appended)
      assert appended is not float_frame
  
      appended = empty._append(float_frame)
      tm.assert_frame_equal(float_frame, appended)
      assert appended is not float_frame
  
imports: import datetime
  from itertools import combinations
  import dateutil
  import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Index, Series, Timestamp, concat, isna
  import pandas._testing
label_desc: Use image node_id 2 for calling the TestAppend obj's underlying member method code with example usage: obj.test_append_empty(float_frame) without return types