code: function createReadFilePromise () {
    return (filepath) => {
      return new Promise((resolve, reject) => {
        fs.readFile(filepath, 'utf8', function (error, data) {
          if (error) {
            reject(new Error(`Cannot read ${filepath}, got: ${error}`))
          } else if (!data) {
            reject(new Error(`No content at ${filepath}`))
          } else {
            resolve(data.split('\n'))
          }
        })
      })
    }
  }
docs: Bind the filesystem into the injectable file reader function