code: def test_astype_to_timedelta_unit(self, unit):
      # coerce to float
      # GH#19223 until 2.0 used to coerce to float
      dtype = f"m8[{unit}]"
      arr = np.array([[1, 2, 3]], dtype=dtype)
      df = DataFrame(arr)
      ser = df.iloc[:, 0]
      tdi = Index(ser)
      tda = tdi._values
  
      if unit in ["us", "ms", "s"]:
          assert (df.dtypes == dtype).all()
          result = df.astype(dtype)
      else:
          # We get the nearest supported unit, i.e. "s"
          assert (df.dtypes == "m8[s]").all()
  
          msg = (
              rf"Cannot convert from timedelta64\[s\] to timedelta64\[{unit}\]. "
              "Supported resolutions are 's', 'ms', 'us', 'ns'"
          )
          with pytest.raises(ValueError, match=msg):
              df.astype(dtype)
          with pytest.raises(ValueError, match=msg):
              ser.astype(dtype)
          with pytest.raises(ValueError, match=msg):
              tdi.astype(dtype)
          with pytest.raises(ValueError, match=msg):
              tda.astype(dtype)
  
          return
  
      result = df.astype(dtype)
      # The conversion is a no-op, so we just get a copy
      expected = df
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import Categorical, CategoricalDtype, DataFrame, DatetimeTZDtype, Index, Interval, IntervalDtype, NaT, Series, Timedelta, Timestamp, concat, date_range, option_context
  import pandas._testing
label_desc: Use image node_id 25 for calling the TestAstype obj's underlying member method code with example usage: obj.test_astype_to_timedelta_unit(unit) without return types