code: def test_assign_order(self):
      # GH 9818
      df = DataFrame([[1, 2], [3, 4]], columns=["A", "B"])
      result = df.assign(D=df.A + df.B, C=df.A - df.B)
  
      expected = DataFrame(
          [[1, 2, 3, -1], [3, 4, 7, -1]], columns=list("ABDC")
      )
      tm.assert_frame_equal(result, expected)
      result = df.assign(C=df.A - df.B, D=df.A + df.B)
  
      expected = DataFrame(
          [[1, 2, -1, 3], [3, 4, -1, 7]], columns=list("ABCD")
      )
  
      tm.assert_frame_equal(result, expected)
  
file_path: pandas/pandas/tests/frame/methods/test_assign.py
imports: import pytest
  from pandas import DataFrame
  import pandas._testing
label_desc: Use image node_id 3 for calling the TestAssign obj's underlying member method code with example usage: obj.test_assign_order() without return types