TST: avoid EncodingWarning

Author: ngoldbaum

pandas/tests/io/test_common.py

@@ -513,19 +513,18 @@ def test_is_fsspec_url_chained():
     assert not icom.is_fsspec_url("filecache::://pandas/test.csv")
 
 
-@pytest.mark.parametrize("encoding", [None, "utf-8"])
 @pytest.mark.parametrize("format", ["csv", "json"])
-def test_codecs_encoding(encoding, format):
+def test_codecs_encoding(format):
     # GH39247
     expected = pd.DataFrame(
         1.1 * np.arange(120).reshape((30, 4)),
         columns=pd.Index(list("ABCD")),
         index=pd.Index([f"i-{i}" for i in range(30)]),
     )
     with tm.ensure_clean() as path:
-        with open(path, mode="w", encoding=encoding) as handle:
+        with open(path, mode="w", encoding="utf-8") as handle:
             getattr(expected, f"to_{format}")(handle)
-        with open(path, encoding=encoding) as handle:
+        with open(path, encoding='utf-8') as handle:
             if format == "csv":
                 df = pd.read_csv(handle, index_col=0)
             else: