Officially you can only have a function with arity 1. There seems to be some support within the code for arity 2 but the Vex.Struct implementation does not use it.
If you follow the Vex.Struct and Vex.Extract.Struct code you may be able to re-implement them to provide your own validates/3 that takes a context, but that would be a more advance solution at the moment.
I respectfully disagree. The Kernel.SpecialForms.&/1 docs say
Capture operator. Captures or creates an anonymous function.
So in this case OP is trying to create an anonymous 2-arity function that calls test/2, but the parsing of @validators is failing because it does seem to expect the form &function/arity
