TST (string dtype): clean up construction of expected string arrays (pandas-dev#59481)

Author: WillAyd

pandas/tests/io/excel/test_readers.py

@@ -659,31 +659,34 @@ def test_dtype_backend_and_dtype(self, read_ext):
     @pytest.mark.xfail(
         using_string_dtype(), reason="infer_string takes precedence", strict=False
     )
-    def test_dtype_backend_string(self, read_ext, string_storage, tmp_excel):
+    def test_dtype_backend_string(self, read_ext, string_storage):
         # GH#36712
         if read_ext in (".xlsb", ".xls"):
             pytest.skip(f"No engine for filetype: '{read_ext}'")
 
-        df = DataFrame(
-            {
-                "a": np.array(["a", "b"], dtype=np.object_),
-                "b": np.array(["x", pd.NA], dtype=np.object_),
-            }
-        )
-        df.to_excel(tmp_excel, sheet_name="test", index=False)
-
         with pd.option_context("mode.string_storage", string_storage):
-            result = pd.read_excel(
-                tmp_excel, sheet_name="test", dtype_backend="numpy_nullable"
+            df = DataFrame(
+                {
+                    "a": np.array(["a", "b"], dtype=np.object_),
+                    "b": np.array(["x", pd.NA], dtype=np.object_),
+                }
             )
 
-        expected = DataFrame(
-            {
-                "a": Series(["a", "b"], dtype=pd.StringDtype(string_storage)),
-                "b": Series(["x", None], dtype=pd.StringDtype(string_storage)),
-            }
-        )
-        tm.assert_frame_equal(result, expected)
+            with tm.ensure_clean(read_ext) as file_path:
+                df.to_excel(file_path, sheet_name="test", index=False)
+                result = pd.read_excel(
+                    file_path, sheet_name="test", dtype_backend="numpy_nullable"
+                )
+
+            expected = DataFrame(
+                {
+                    "a": Series(["a", "b"], dtype=pd.StringDtype(string_storage)),
+                    "b": Series(["x", None], dtype=pd.StringDtype(string_storage)),
+                }
+            )
+            # the storage of the str columns' Index is also affected by the
+            # string_storage setting -> ignore that for checking the result
+            tm.assert_frame_equal(result, expected, check_column_type=False)
 
     @pytest.mark.parametrize("dtypes, exp_value", [({}, 1), ({"a.1": "int64"}, 1)])
     def test_dtype_mangle_dup_cols(self, read_ext, dtypes, exp_value):