Hi @epustovaya,
In general the code looks good! What you are missing is a renderer which is able to handle the VerticalLayout.
JSON Forms will encounter the VerticalLayout first and will try to find a renderer for it. However you only hand over the {fieldInputTester, FieldInputControl} which will return not applicable (i.e. -1). Therefore there is no renderer for VerticalLayout found and JSON Forms will output the error message instead.
See here for an example for a VerticalLayout renderer.