Stop a node server in Travis CI

So, my code contains unit tests that require a server. So I have sever up and running, my tests pass, but the problem is that I don't know how to stop server, so my build fails because it gets timed out.

Here is my configuration file

language: node_js
node_js:
 - "7.10.0"
services:
 - mongodb
env:
 - PORT=6655 IP="localhost" NODE_ENV="test"
script: 
 - npm start &
 - sleep 25
 - npm test

Now, how do I stop the node server?

Edit: Here are my npm scripts

  "scripts": {
    "build-js": "webpack --config webpack.config.js",
    "test": "node node_modules/.bin/mocha ./server/test  --require ./server/test/testHelper.js --watch  --reporter spec --timeout 10000 --compilers js:babel-core/register",
    "start": "npm run build-js && babel-node app.js myApp --presets es2015,stage-2 && nodemon --watch cms/client",
  }