version: '2'

services:
  app:
    build:
      context: ../../
    expose:
      - "3000"
    command: npm run start

  selenium:
    image: selenium/standalone-chrome
    expose:
      - '4444'
    links:
      - app

  tests:
    extends:
      service: app
    links:
      - selenium
    command: npm run _test:acceptance

version: '2'

services:
  app:
    build:
      context: ../../
    expose:
      - '3000'
    command: npm run start

  selenium:
    image: selenium/standalone-chrome
    expose:
      - '4444'
    links:
      - app

  tests:
    extends:
      service: app
    links:
      - selenium
    command: npm run _test:acceptance

Use single quotes in YAML files
Use single quotes in YAML files
