Restrict the roles with ""Test as another role"" option

Test As Role is not intended for that purpose.  It will always allow all Roles.

You should focus on the app behavior you are trying to achieve for that special person who does a job which crosses two Roles.  Note that Users may be in multiple Roles.  The user will see the dash word and tables of the First Role they are in, according to the listed sequence of the Roles (which you can drag and drop to sequence) and that user would have the MOST permissions possible based in both roles.