testament: error instead of silently overwrite a spec (#16166)

tests/generics/tmetafield.nim

@@ -1,10 +1,23 @@
 discard """
   cmd: "nim check $options $file"
-  errormsg: "'proc' is not a concrete type"
-  errormsg: "'Foo' is not a concrete type."
-  errormsg: "invalid type: 'proc' in this context: 'TBaseMed'"
+  action: "reject"
+  nimout: '''
+tmetafield.nim(26, 5) Error: 'proc' is not a concrete type; for a callback without parameters use 'proc()'
+tmetafield.nim(27, 5) Error: 'Foo' is not a concrete type
+tmetafield.nim(29, 5) Error: invalid type: 'proc' in this context: 'TBaseMed' for var
+'''
 """
 
+# bug #188
+
+
+
+
+
+
+
+
+# line 20
 type
   Foo[T] = object
     x: T
@@ -15,4 +28,3 @@ type
 
 var a: TBaseMed
 
-# issue 188