Add Snapshot testing

[DawoodShahat]

This PR fixes #117

Pull Request checklist

• The pull request has a descriptive title (and a reference to an issue it
  fixes, if applicable)
• All tests and linter checks are passing
• The pull request is free of merge conflicts

[wlach]

This looks great @DawoodShahat! I have some concerns about modifying the svelte files, but other than that this is looking very close.

Checking the CI logs, I noticed this warning:

    console.warn
      <FilterInput> was created without expected prop 'filterText'



      at new FilterInput (src/components/FilterInput.svelte:132:12)
      at create_fragment (stories/FilterableList.svelte:56:16)
      at init (node_modules/svelte/internal/index.js:1465:37)
      at new FilterableList (stories/FilterableList.svelte:193:3)
      at getRenderedTree (node_modules/@storybook/addon-storyshots/dist/frameworks/svelte/renderTree.js:20:5)
      at node_modules/@storybook/addon-storyshots/dist/test-bodies.js:11:22
      at Object.<anonymous> (node_modules/@storybook/addon-storyshots/dist/api/snapshotsTestsTemplate.js:42:20)

It looks like maybe the story is lacking something? It would be good if we could make issues like that fail the CI, as they often indicate bugs.

[wlach]

With lodash we can just do:

Suggested change

	const throttle = require("just-throttle");
	import { throttle } from "lodash";

... and it'll work

[wlach]

Suggested change

	const marked = require("marked");
	import { parseInline } from "marked";

[DawoodShahat]

Here is what I updated upon @wlach review:

• Removed just-throttle dependency and instead used _throttle from lodash
• Fixed the warning that was generated by FilterInput.svelte component
• Used ES6 imports instead of CJS require

The CI will now fail when there is an unintended change in the markup. I think we should update the README and add some instructions on how to update the generated snapshots with your intended changes e.g. npm run test:jest -- -u.

Also one more thing, What do you think about deploying Stories to netlify?

By the way thanks for the review, I spent a good amount of time on the error.

[wlach]

The CI will now fail when there is an unintended change in the markup. I think we should update the README and add some instructions on how to update the generated snapshots with your intended changes e.g. npm run test:jest -- -u.

Great idea, could you add something about this to the README? I think we can add them to the storybook: https://github.com/mozilla/glean-dictionary#storybook

Also one more thing, What do you think about deploying Stories to netlify?

This is also a great idea! I think we could probably publish a static copy to /storybook/. I would obviously do this in a followup.

[wlach]

Code looks great, I think we just need an update to the README and we'll be good to land.

[wlach]

Great stuff, just have some minor suggested changes to the README which I'll apply before landing.