Add Jest for Vue testing

Add Jest for Vue testing.

I went with Jest over trying to shove something into Mocha because I kept running into roadblocks and the shoddy setup didn't seem nice.

Part of https://gitlab.com/gitlab-org/gitter/webapp/merge_requests/1360

npm run jest

npm run jest -- test/public-js/vue/left-menu/components/index-test.js

• https://vue-test-utils.vuejs.org/guides/#testing-single-file-components-with-jest
• Also based off of gitlab-ce, https://gitlab.com/gitlab-org/gitlab-ce/tree/6418ffacfaf9394391b4662a97abc57e8fd78f9b/

Testing notes

Jest

• Aligns with what GitLab is moving forward with
• https://vue-test-utils.vuejs.org/guides/#testing-single-file-components-with-jest
• Built in snapshotting

Mocha

• https://vue-test-utils.vuejs.org/guides/testing-single-file-components-with-mocha-webpack.html
• mocha-webpack
• Using https://github.com/bahmutov/snap-shot-it
  • Running into TypeError: Converting circular structure to JSON when trying to snapshot(vm.element);
• Requires yet another webpack config
  • https://github.com/zinserjan/mocha-webpack/issues/317
• Using beta version mocha-webpack@2.0.0-beta.0 for webpack 4 support and project hasn't been touched in a year

You can see my attempt here, https://gitlab.com/gitlab-org/gitter/webapp/merge_requests/1360/diffs?commit_id=012a09443ae36ae4c2162f188667e4afbd9ab540

• https://medium.com/blogfoster-engineering/how-to-use-the-power-of-jests-snapshot-testing-without-using-jest-eff3239154e5
  • Doesn't account for .vue files and transpiling