code: def test_append_length0_frame(self, sort):
      df = DataFrame(columns=["A", "B", "C"])
      df3 = DataFrame(index=[0, 1], columns=["A", "B"])
      df5 = df._append(df3, sort=sort)
  
      expected = DataFrame(index=[0, 1], columns=["A", "B", "C"])
      tm.assert_frame_equal(df5, expected)
  
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 5 for calling the TestAppend obj's underlying member method code with example usage: obj.test_append_length0_frame(sort) without return types