Actually exercise Validator.is_type on an unknown type.

Author: Julian

jsonschema/tests/test_types.py

@@ -190,3 +190,8 @@ def test_object_extensions_can_handle_custom_validators(self):
 
         with self.assertRaises(ValidationError):
             validator.validate(Point(x="not an integer", y=5))
+
+    def test_unknown_type(self):
+        with self.assertRaises(UnknownType) as e:
+            Draft4Validator({}).is_type(12, "some unknown type")
+        self.assertIn("'some unknown type'", str(e.exception))