Example of using `allOf` to extend an object in a Swagger API

NewsArticle.yaml

swagger: "2.0"
info:
  version: "1.0.0"
  title: minimal
  description: News Articles ftw
paths:
  /users:
    get:
      responses:
        "200":
          description:  hello world
definitions:
  NewsArticle:
      title: NewsArticle
      type: object
      properties:
          id:
              type: integer
              format: int32
              x-mysql-type: int(11)
  NewsArticleExt: # tmp
      title: NewsArticleExt
      type: object
      allOf:
          - $ref: "#/definitions/NewsArticle"
          - properties:
              test:
                  type: string

  Pet:
    allOf:
      - $ref: '#/definitions/NewPet'
    required:
      - id
    properties:
      id:
        type: integer
        format: int64

  NewPet:
    required:
      - name  
    properties:
      name:
        type: string
      tag:
        type: string

Actually this should be something like this

swagger: "2.0"
info:
  version: "1.0.0"
  title: minimal
  description: News Articles ftw
paths:
  /users:
    get:
      responses:
        "200":
          description:  hello world
definitions:
  NewsArticle:
      title: NewsArticle
      type: object
      properties:
          id:
              type: integer
              format: int32
              x-mysql-type: int(11)
  NewsArticleExt: # tmp
      title: NewsArticleExt
      type: object
      allOf:
          - $ref: "#/definitions/NewsArticle"
          - type: object
            properties:
              test:
                  type: string

Lol, in your examples the /users path items has no schema defined, so are not calling any of the definitions...