TST: add test for dtype argument in str.decode (#61872)

Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>

Author: hippowm

pandas/tests/strings/test_strings.py

@@ -11,6 +11,7 @@
     Index,
     MultiIndex,
     Series,
+    option_context,
 )
 import pandas._testing as tm
 from pandas.core.strings.accessor import StringMethods
@@ -778,3 +779,11 @@ def test_series_str_decode():
     result = Series([b"x", b"y"]).str.decode(encoding="UTF-8", errors="strict")
     expected = Series(["x", "y"], dtype="str")
     tm.assert_series_equal(result, expected)
+
+
+def test_decode_with_dtype_none():
+    with option_context("future.infer_string", True):
+        ser = Series([b"a", b"b", b"c"])
+        result = ser.str.decode("utf-8", dtype=None)
+        expected = Series(["a", "b", "c"], dtype="str")
+        tm.assert_series_equal(result, expected)