Response schema for text/csv

I have a couple of questions for specifying the response format:

 

(1) If you specify a "text/csv" mime type and then specify a nested object as the response schema, what's the output supposed to look like? For example, if you 'User' below as a text/csv response, what should the csv look like?

components:
  schemas:
    User:
      type: object
      properties:
        id:
          type: integer
        name:
          type: string
        contact_info:
          $ref: '#/components/schemas/ContactInfo'
    ContactInfo:
      type: object
      properties:
        email:
          type: string
          format: email
        phone:
          type: string

(2) Is there some tool that will validate a response body (or maybe just a file) against the schema defined? It would be handy to be able to test that output is actually valid.