a.yaml

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Test
servers:
  - url: http://localhost/
paths:
  /test:
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Test"
      responses:
        '200':
          description: test
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Test"
components:
  schemas:
    Test:
      enum: ["A", "B"]