Ensuring typesafe

how can I ensure, the function execution result returns same type as mentioned in the function?

 

let
    test_type = () as text=> "Hello",
    tbl = #table(type table [Name = text, Score = number], {{"Betty", 90.3}, {"Carl", 89.5}}),
    #"Added Custom" = Table.AddColumn(tbl, "Custom", each test_type())
    /*want to avoid doing below and the type needs to cascade from the function*/
    /*Table.AddColumn(tbl, "Custom", each test_type(), type text)*/
in
    #"Added Custom"

 

getting this

desire this

without requiring to do this

Table.AddColumn(tbl, "Custom", each test_type(), type text)

 AlexisOlson ImkeF