code: def test_astype_roundtrip(dtype):
      ser = pd.Series(pd.date_range("2000", periods=12))
      ser[0] = None
  
      casted = ser.astype(dtype)
      assert is_dtype_equal(casted.dtype, dtype)
  
      result = casted.astype("datetime64[ns]")
      tm.assert_series_equal(result, ser)
  
      # GH#38509 same thing for timedelta64
      ser2 = ser - ser.iloc[-1]
      casted2 = ser2.astype(dtype)
      assert is_dtype_equal(casted2.dtype, dtype)
  
      result2 = casted2.astype(ser2.dtype)
      tm.assert_series_equal(result2, ser2)
  
imports: import operator
  import numpy
  import pytest
  from pandas.compat.pyarrow import pa_version_under12p0
  from pandas.core.dtypes.common import is_dtype_equal
  import pandas
  import pandas._testing
  from pandas.core.arrays.string_arrow import ArrowStringArray, ArrowStringArrayNumpySemantics
label_desc: Use image node_id 9 for calling a global function with example usage: test_astype_roundtrip(dtype) without return types