code: def test_append_empty_frame_with_timedelta64ns_nat(
      self, dtype_str, val
  ):
      # https://github.com/pandas-dev/pandas/issues/35460
      df = DataFrame(columns=["a"]).astype(dtype_str)
  
      other = DataFrame({"a": [np.timedelta64(val, "ns")]})
      result = df._append(other, ignore_index=True)
  
      expected = other.astype(object)
      if isinstance(val, str) and dtype_str != "int64":
          # TODO: expected used to be `other.astype(object)` which is a more
          #  reasonable result.  This was changed when tightening
          #  assert_frame_equal's treatment of mismatched NAs to match the
          #  existing behavior.
          expected = DataFrame({"a": [np.nan]}, dtype=object)
      tm.assert_frame_equal(result, 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 17 for calling the TestAppend obj's underlying member method code with example usage: obj.test_append_empty_frame_with_timedelta64ns_nat(dtype_str, val) without return types