How to stop npm start , when lint or Unit testcase fails?

I am using npm start with lint and unit test case, if lint or test case fails, npm should not up the api, but I am not able to do.

Here is code I am using:

"scripts": {
    "start": "gulp lint & npm test & node src/server/index.js",
    "test": "mocha --timeout 10000"
  },

Please help me what I have to do for it, I searched on internet also, but not getting the proper solution.

via Anita Mehta