the configuration is as follows. What else do I need to change? English is not good. I only understand so much when I read the transfer documents.

-sharp Javascript Node CircleCI 2.0 configuration file
-sharp
-sharp Check https://circleci.com/docs/2.0/language-javascript/ for more details
-sharp
version: 2
jobs:
  build:
    docker:
      -sharp specify the version you desire here
      - image: circleci/node:8.9.4
      
      -sharp Specify service dependencies here if necessary
      -sharp CircleCI maintains a library of pre-built images
      -sharp documented at https://circleci.com/docs/2.0/circleci-images/
      -sharp - image: circleci/mongo:3.4.4

    working_directory: ~/repo

    steps:
      - checkout

      -sharp Download and cache dependencies
      - restore_cache:
          keys:
          - dependencies-{{ checksum "package.json" }}

      - run: yarn install

      - save_cache:
          paths:
            - node_modules
          key: dependencies-{{ checksum "package.json" }}
        
      -sharp run tests!  
      - run: npm run test