Fixed frozenset not being checked

Fixes #367.

docs/versionhistory.rst

@@ -15,6 +15,8 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 - Fixed ``@typechecked`` failing to instrument functions when there are more than one
   function within the same scope
   (`#355 <https://github.com/agronholm/typeguard/issues/355>`_)
+- Fixed ``frozenset`` not being checked
+  (`#367 <https://github.com/agronholm/typeguard/issues/367>`_)
 
 **4.0.0** (2023-05-12)
 

src/typeguard/_checkers.py

@@ -316,7 +316,10 @@ def check_set(
     args: tuple[Any, ...],
     memo: TypeCheckMemo,
 ) -> None:
-    if not isinstance(value, AbstractSet):
+    if origin_type is frozenset:
+        if not isinstance(value, frozenset):
+            raise TypeCheckError("is not a frozenset")
+    elif not isinstance(value, AbstractSet):
         raise TypeCheckError("is not a set")
 
     if args and args != (Any,):
@@ -794,6 +797,7 @@ def check_type_internal(
     dict: check_mapping,
     Dict: check_mapping,
     float: check_number,
+    frozenset: check_set,
     IO: check_io,
     list: check_list,
     List: check_list,

tests/test_checkers.py

@@ -15,6 +15,7 @@
     ContextManager,
     Dict,
     ForwardRef,
+    FrozenSet,
     Iterator,
     List,
     Mapping,
@@ -606,6 +607,38 @@ def test_full_check_fail(self):
         ).match("set is not an instance of int")
 
 
+class TestFrozenSet:
+    def test_bad_type(self):
+        pytest.raises(TypeCheckError, check_type, 5, FrozenSet[int]).match(
+            "int is not a frozenset"
+        )
+
+    def test_valid(self):
+        check_type(frozenset({1, 2}), FrozenSet[int])
+
+    def test_first_check_empty(self):
+        check_type(frozenset(), FrozenSet[int])
+
+    def test_first_check_fail(self, sample_set: set):
+        pytest.raises(
+            TypeCheckError, check_type, frozenset(sample_set), FrozenSet[int]
+        ).match("set is not an instance of int")
+
+    def test_full_check_fail(self):
+        pytest.raises(
+            TypeCheckError,
+            check_type,
+            frozenset({1, 2, "bb"}),
+            FrozenSet[int],
+            collection_check_strategy=CollectionCheckStrategy.ALL_ITEMS,
+        ).match("set is not an instance of int")
+
+    def test_set_against_frozenset(self, sample_set: set):
+        pytest.raises(TypeCheckError, check_type, sample_set, FrozenSet[int]).match(
+            "set is not a frozenset"
+        )
+
+
 @pytest.mark.parametrize(
     "annotated_type",
     [