Replace Karma with Vitest for JavaScript testing

[milmazz]

This PR mainly tackles the following issues:

• Replace Karma, which is deprecated, with a modern testing framework such as Vitest. Vitest provides native ESM support, jsdom for DOM testing, and eliminates the need for Chrome and xvfb-run in CI.
• While I was working on this, I updated other JS dependencies to fix some vulnerabilities

Karma -> Vitest

• Remove karma, karma-*, and mocha dependencies
• Add vitest and jsdom
• Translate Chai BDD assertions to Vitest matchers
• Rename Mocha before to Vitest beforeAll
• Simplify CI workflow by removing xvfb/Chrome setup

While we don't have a huge suite of tests for JS, we went from 17s to 2s when we run npm run --prefix assets test via CI.

Package updates

When I ran:

$ npm install --prefix assets                                                                                                                                                                                                                                                                                                              (base)
npm WARN deprecated glob@8.1.0: Glob versions prior to v9 are no longer supported
npm WARN deprecated text-encoding@0.6.4: no longer maintained
npm WARN deprecated samsam@1.3.0: This package has been deprecated in favour of @sinonjs/samsam
npm WARN deprecated formatio@1.2.0: This package is unmaintained. Use @sinonjs/formatio instead

added 117 packages, removed 1545 packages, changed 204 packages, and audited 366 packages in 4s

98 packages are looking for funding
  run `npm fund` for details

7 vulnerabilities (2 low, 5 high)

After running npm audit fix --prefix assets I got:

$ npm audit fix --prefix assets                                                                                                                                                                                                                                                                                                                (base)

added 2 packages, removed 2 packages, changed 9 packages, and audited 366 packages in 847ms

98 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities

[github-actions]

📦 Docs artifacts are ready: https://github.com/elixir-lang/ex_doc/actions/runs/21813962467/artifacts/5427535723

[milmazz]

This new script will allow developers to track coverage in case they want to verify or improve our current testing suite.

This is the current report in case you're curious:

npm run --prefix assets test:coverage                                                                                                                  (base)

> test:coverage
> vitest run --coverage


 RUN  v3.2.4 /Users/milmazz/Dev/elixir-lang/ex_doc/assets
      Coverage enabled with v8

 ✓ test/helpers.spec.js (1 test) 2ms
 ✓ test/autocomplete/suggestions.spec.js (16 tests) 6ms
 ✓ test/tooltips/hints.spec.js (2 tests) 7ms

 Test Files  3 passed (3)
      Tests  19 passed (19)
   Start at  23:45:56
   Duration  563ms (transform 39ms, setup 0ms, collect 67ms, tests 15ms, environment 628ms, prepare 127ms)

 % Coverage report from v8
----------------------------|---------|----------|---------|---------|----------------------------------------------------------------------
File                        | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------------------------|---------|----------|---------|---------|----------------------------------------------------------------------
All files                   |   17.22 |    68.46 |   37.14 |   17.22 |
 js                         |     7.3 |    21.73 |    12.5 |     7.3 |
  constants.js              |       0 |        0 |       0 |       0 | 1-7
  content.js                |       0 |        0 |       0 |       0 | 1-24
  copy-button.js            |       0 |        0 |       0 |       0 | 1-45
  copy-markdown.js          |       0 |        0 |       0 |       0 | 1-64
  globals.js                |   81.81 |    33.33 |      50 |   81.81 | 14-15
  helpers.js                |   53.24 |      100 |   21.42 |   53.24 | 46-47,58-128,137-139,154-157,166-171,192-202,210-211,219-221,232-242
  keyboard-shortcuts.js     |       0 |        0 |       0 |       0 | 1-126
  makeup.js                 |       0 |        0 |       0 |       0 | 1-28
  modal.js                  |       0 |        0 |       0 |       0 | 1-98
  quick-switch.js           |       0 |        0 |       0 |       0 | 1-239
  search-bar.js             |       0 |        0 |       0 |       0 | 1-335
  search-page.js            |       0 |        0 |       0 |       0 | 1-302
  settings-store.js         |       0 |        0 |       0 |       0 | 1-122
  settings.js               |       0 |        0 |       0 |       0 | 1-105
  swup.js                   |       0 |        0 |       0 |       0 | 1-40
  tabsets.js                |       0 |        0 |       0 |       0 | 1-147
  theme.js                  |       0 |        0 |       0 |       0 | 1-34
  toast.js                  |       0 |        0 |       0 |       0 | 1-25
 js/autocomplete            |   74.11 |    93.24 |   95.23 |   74.11 |
  autocomplete-list.js      |       0 |        0 |       0 |       0 | 1-108
  suggestions.js            |    98.9 |    94.52 |     100 |    98.9 | 154,183-184
 js/entry                   |       0 |        0 |       0 |       0 |
  epub.js                   |       0 |        0 |       0 |       0 | 1-6
  html.js                   |       0 |        0 |       0 |       0 | 1-19
  inline_html.js            |       0 |        0 |       0 |       0 | 1-34
 js/handlebars              |       0 |        0 |       0 |       0 |
  helpers.js                |       0 |        0 |       0 |       0 | 1-17
 js/sidebar                 |       0 |        0 |       0 |       0 |
  constants.js              |       0 |        0 |       0 |       0 | 1-7
  sidebar-drawer.js         |       0 |        0 |       0 |       0 | 1-128
  sidebar-list.js           |       0 |        0 |       0 |       0 | 1-263
  sidebar-version-select.js |       0 |        0 |       0 |       0 | 1-126
 js/tooltips                |   31.23 |    33.33 |   22.22 |   31.23 |
  hint-page.js              |       0 |        0 |       0 |       0 | 1-35
  hints.js                  |   66.24 |       50 |   28.57 |   66.24 | 51-63,73-80,88-91,99-133,139-142
  tooltips.js               |       0 |        0 |       0 |       0 | 1-177
----------------------------|---------|----------|---------|---------|----------------------------------------------------------------------

While the console report is a bit verbose, the tested modules have good coverage:

• js/autocomplete/suggestions.js — 98.9% statements
• js/globals.js — 81.8% statements
• js/tooltips/hints.js — 66.2% statements
• js/helpers.js — 53.2% statements

Overall is 17.2% across all 39 JS files, reflecting that only 3 modules are currently tested.

The command also provides an alternative view that you can browse by opening: assets/coverage/index.html

[josevalim]

Beautiful!!!!