code: def test_dtype_backend(string_storage, dtype_backend):
      # GH#50289
      if string_storage == "python":
          arr = StringArray(np.array(["a", "b"], dtype=np.object_))
          arr_na = StringArray(np.array([pd.NA, "a"], dtype=np.object_))
      elif dtype_backend == "pyarrow":
          pa = pytest.importorskip("pyarrow")
          from pandas.arrays import ArrowExtensionArray
  
          arr = ArrowExtensionArray(pa.array(["a", "b"]))
          arr_na = ArrowExtensionArray(pa.array([None, "a"]))
      else:
          pa = pytest.importorskip("pyarrow")
          arr = ArrowStringArray(pa.array(["a", "b"]))
          arr_na = ArrowStringArray(pa.array([None, "a"]))
  
      data = """a  b    c      d  e     f  g    h  i
  1  2.5  True  a
  3  4.5  False b  True  6  7.5  a"""
      with pd.option_context("mode.string_storage", string_storage):
          result = read_fwf(StringIO(data), dtype_backend=dtype_backend)
  
      expected = DataFrame(
          {
              "a": pd.Series([1, 3], dtype="Int64"),
              "b": pd.Series([2.5, 4.5], dtype="Float64"),
              "c": pd.Series([True, False], dtype="boolean"),
              "d": arr,
              "e": pd.Series([pd.NA, True], dtype="boolean"),
              "f": pd.Series([pd.NA, 6], dtype="Int64"),
              "g": pd.Series([pd.NA, 7.5], dtype="Float64"),
              "h": arr_na,
              "i": pd.Series([pd.NA, pd.NA], dtype="Int64"),
          }
      )
      if dtype_backend == "pyarrow":
          pa = pytest.importorskip("pyarrow")
          from pandas.arrays import ArrowExtensionArray
  
          expected = DataFrame(
              {
                  col: ArrowExtensionArray(
                      pa.array(expected[col], from_pandas=True)
                  )
                  for col in expected.columns
              }
          )
          expected["i"] = ArrowExtensionArray(pa.array([None, None]))
  
      tm.assert_frame_equal(result, expected)
  
imports: from datetime import datetime
  from io import BytesIO, StringIO
  from pathlib import Path
  import numpy
  import pytest
  from pandas.errors import EmptyDataError
  import pandas
  from pandas import DataFrame, DatetimeIndex
  import pandas._testing
  from pandas.core.arrays import ArrowStringArray, StringArray
  from pandas.io.common import urlopen
  from pandas.io.parsers import read_csv, read_fwf
label_desc: Use image node_id 42 for calling a global function with example usage: test_dtype_backend(string_storage, dtype_backend) without return types