TST: read_fwf with dtype_backend (#50911)

Co-authored-by: Patrick Hoefler <[email protected]>

Author: mroeschke

doc/source/whatsnew/v2.0.0.rst

@@ -54,6 +54,7 @@ to select the nullable dtypes implementation.
 
 * :func:`read_csv` (with ``engine="pyarrow"`` or ``engine="python"``)
 * :func:`read_clipboard` (with ``engine="python"``)
+* :func:`read_fwf`
 * :func:`read_excel`
 * :func:`read_html`
 * :func:`read_xml`

pandas/tests/io/parser/test_read_fwf.py

@@ -948,24 +948,27 @@ def test_widths_and_usecols():
     tm.assert_frame_equal(result, expected)
 
 
-def test_use_nullable_dtypes(string_storage):
+@pytest.mark.parametrize("dtype_backend", ["pandas", "pyarrow"])
+def test_use_nullable_dtypes(string_storage, dtype_backend):
     # GH#50289
 
-    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), use_nullable_dtypes=True)
+    if string_storage == "pyarrow" or dtype_backend == "pyarrow":
+        pa = pytest.importorskip("pyarrow")
 
     if string_storage == "python":
         arr = StringArray(np.array(["a", "b"], dtype=np.object_))
         arr_na = StringArray(np.array([pd.NA, "a"], dtype=np.object_))
     else:
-        import pyarrow as pa
-
         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):
+        with pd.option_context("mode.dtype_backend", dtype_backend):
+            result = read_fwf(StringIO(data), use_nullable_dtypes=True)
+
     expected = DataFrame(
         {
             "a": pd.Series([1, 3], dtype="Int64"),
@@ -979,4 +982,15 @@ def test_use_nullable_dtypes(string_storage):
             "i": pd.Series([pd.NA, pd.NA], dtype="Int64"),
         }
     )
+    if dtype_backend == "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)