ERROR in Cannot find module 'node-sass'

Running npm test after a successful npm install:

angular-webpack@1.0.0 test /Users/kevins/src/angular-webpack
karma start ./karma.conf.js --single-run

Hash: 4a4605458275acc8826d
Version: webpack 1.14.0
Time: 45ms
webpack: bundle is now VALID.
webpack: bundle is now INVALID.
Hash: d105a25e47b9a4281cc8
Version: webpack 1.14.0
Time: 2529ms
  Asset     Size  Chunks             Chunk Names
spec.js  1.43 MB       0  [emitted]  spec.js
chunk    {0} spec.js (spec.js) 1.33 MB [rendered]

ERROR in Cannot find module 'node-sass'
 @ ./src/hello/hello.sass 4:14-162
webpack: bundle is now VALID.
01 02 2017 08:55:40.906:INFO [karma]: Karma v0.13.22 server started at http://localhost:9876/
01 02 2017 08:55:40.922:INFO [launcher]: Starting browser PhantomJS
01 02 2017 08:55:41.046:ERROR [launcher]: Cannot start PhantomJS

01 02 2017 08:55:41.052:INFO [launcher]: Trying to start PhantomJS again (1/2).
01 02 2017 08:55:41.176:ERROR [launcher]: Cannot start PhantomJS

01 02 2017 08:55:41.177:INFO [launcher]: Trying to start PhantomJS again (2/2).
01 02 2017 08:55:41.292:ERROR [launcher]: Cannot start PhantomJS

01 02 2017 08:55:41.294:ERROR [launcher]: PhantomJS failed 2 times (cannot start). Giving up.
npm ERR! Test failed.  See above for more details.