diff --git a/spec/core/types/strings.json b/spec/core/types/strings.json
index 49389c276e39d4f84ebc3a0185914f2b326ddcc9..f4dbe4e87dbe9d7b2c735e03275c6b5170fa8b93 100644
--- a/spec/core/types/strings.json
+++ b/spec/core/types/strings.json
@@ -111,7 +111,8 @@
               "type": "string",
               "format": "unknown"
             }
-          }
+          },
+          "required": ["test"]
         },
         "throws": "unknown generator for .+? in \\/properties\\/test"
       },
@@ -124,7 +125,8 @@
               "type": "string",
               "faker": "not.exists"
             }
-          }
+          },
+          "required": ["test"]
         },
         "throws": "unknown faker-generator for .+? in \\/properties\\/test"
       }