feat: Add Vitest + React Testing Library for frontend unit testing

[Shruti2110-coder]

Summary

The Karmada Dashboard frontend (under ui/) currently has no unit test setup. I'd like to propose adding Vitest + React Testing Library for component-level unit testing.

Why this matters

• The ui/ directory has grown with React + TypeScript components but has zero automated test coverage
• Vitest is the standard testing tool for Vite-based projects (which this project uses)
• Unit tests would help catch regressions in core UI components like cluster management, policy views, etc.
• This is a commonly requested improvement in CNCF dashboard projects

What I propose to do

1. Add `vitest, @testing-library/react, @testing-library/jest-dom, and jsdom as dev dependencies
2. Configure Vitest inside the existing vite.config.ts
3. Create a src/test/setup.ts setup file
4. Write initial unit tests for 2–3 core components (e.g. login page, cluster list, navigation)
5. Add a "test" script to package.json

Scope

This is frontend-only and does not touch the Go backend. The goal is to establish a baseline test setup so future contributors can add tests alongside new components.

Question for maintainers

Are you open to this? If yes, are there specific components you'd like tested first, or any conventions I should follow?

[warjiang]

cool, maybe we can have a short discussion about that ~

[Shruti2110-coder]

happy to have discussion
To get us started, here's roughly where my head's at:

Config straight into vite.config.ts, no separate vitest.config.ts
src/test/setup.ts for jest-dom matchers + any global mocks
"test": "vitest run" script in package.json
For first tests, thinking cluster list rendering, a form/login component, and nav — but happy to follow your lead if there's somewhere else you'd rather see covered first
Curious on your take re: mocking API calls (msw vs manual) and whether test should run in CI right away or as a follow-up