code: def test_frame_astype_no_copy():
      # GH 42501
      df = DataFrame(
          {"a": [1, 4, None, 5], "b": [6, 7, 8, 9]}, dtype=object
      )
      result = df.astype({"a": Int16DtypeNoCopy()}, copy=False)
  
      assert result.a.dtype == pd.Int16Dtype()
      assert np.shares_memory(df.b.values, result.b.values)
  
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 2 for calling a global function with example usage: test_frame_astype_no_copy() without return types