diff --git a/tests/test_forms.py b/tests/test_forms.py
index b00ce7c..33fa264 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -12,6 +12,7 @@
         "d": typesystem.Choice(
             choices=[("abc", "Abc"), ("def", "Def"), ("ghi", "Ghi")]
         ),
+        "extra": typesystem.Boolean(default=True, read_only=True),
         "password": typesystem.Password(),
     }
 )