feat: PropertiesList can now behave as an iterable (#2345)

* Define iterable behaviour for `PropertiesList`

* Add `Returns:` to docstring

* Add test

singer_sdk/typing.py

@@ -1017,6 +1017,14 @@ def append(self, property: Property) -> None:  # noqa: A002
         """
         self.wrapped[property.name] = property
 
+    def __iter__(self) -> t.Iterator[Property]:
+        """Iterate all properties of the property list.
+
+        Returns:
+            Iterator of properties.
+        """
+        return self.wrapped.values().__iter__()
+
 
 def to_jsonschema_type(
     from_type: str | sa.types.TypeEngine | type[sa.types.TypeEngine],

tests/core/test_typing.py

@@ -349,3 +349,15 @@ def test_to_sql_type(jsonschema_type, expected):
 def test_append_null(type_dict: dict, expected: dict):
     result = append_type(type_dict, "null")
     assert result == expected
+
+
+def test_iterate_properties_list():
+    primitive_property = Property("primitive", BooleanType)
+    object_property = Property("object", PropertiesList(Property("value", BooleanType)))
+    list_property = Property("list", ArrayType(BooleanType))
+
+    properties_list = PropertiesList(primitive_property, object_property, list_property)
+
+    assert primitive_property in properties_list
+    assert object_property in properties_list
+    assert list_property in properties_list