a.yaml

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
  license:
    name: MIT
servers:
  - url: http://petstore.swagger.io/v1
paths:
  /test:
    post:
      requestBody:
        content:
          "application/json" :
            schema:
              type: "string"
        required: false
      responses:
        "200":
          description: "Test"
components: {}