BUG/TST: fixed series apply frozenset error and created test case (#903)

* fixed series apply frozenset error and created test case

* added test function for series.apply and removed incorrect test

* added new line after last test

* fixed tests to adhere to check & assert_type way of testing

* fixed pre-commit black issues

* fixed test formatting

* fixed black error in series.pyi

pandas-stubs/core/series.pyi

@@ -940,7 +940,9 @@ class Series(IndexOpsMixin[S1], NDFrame):
     @overload
     def apply(
         self,
-        func: Callable[..., Scalar | Sequence | set | Mapping | NAType | None],
+        func: Callable[
+            ..., Scalar | Sequence | set | Mapping | NAType | frozenset | None
+        ],
         convertDType: _bool = ...,
         args: tuple = ...,
         **kwds,

tests/test_series.py

@@ -3083,3 +3083,11 @@ def first_arg_not_series(argument_1: int, ser: pd.Series) -> pd.Series:
             ),
             1,
         )
+
+
+def test_series_apply() -> None:
+    s = pd.Series(["A", "B", "AB"])
+    check(assert_type(s.apply(tuple), "pd.Series[Any]"), pd.Series)
+    check(assert_type(s.apply(list), "pd.Series[Any]"), pd.Series)
+    check(assert_type(s.apply(set), "pd.Series[Any]"), pd.Series)
+    check(assert_type(s.apply(frozenset), "pd.Series[Any]"), pd.Series)