feat: Add a unit test target (jest) to the UI extension and run it in CI (#1192)

- Introduce test targets.
- Adding additional tests.

Related to: https://github.com/harvester/harvester/issues/11892

Signed-off-by: Volker Theile <vtheile@suse.com>

docs/agents.md/agents/tools.md

@@ -15,6 +15,8 @@
 | `yarn serve-pkgs` | Serve the locally built extension for testing |
 | `yarn lint` | Run ESLint (zero warnings allowed) |
 | `yarn lint:fix` | Run ESLint with auto-fix |
+| `yarn test` | Run the unit tests (Jest) in watch mode |
+| `yarn test:ci` | Run the unit tests once, as CI does (silent) |
 | `yarn clean` | Clean build artifacts |
 | `yarn agents:generate` | Regenerate `AGENTS.md` from `docs/agents.md/` sources |
 
@@ -51,6 +53,16 @@
 - ESLint covers `.js`, `.ts`, and `.vue` files.
 - Always run `yarn lint:fix` before committing.
 
+### Unit Tests
+
+- **Run**:
+  ```bash
+  yarn test
+  ```
+  - `yarn test` starts Jest in watch mode (like in the Rancher dashboard) and only runs the tests related to changed files. It does not exit, so use `yarn test:ci` for a single run of all tests, e.g. in scripts.
+- CI runs `yarn test:ci` on every pull request.
+- See the Unit Tests section of the Contributors Guide for how the tests are set up.
+
 ### Commit Conventions
 
 - Commits are validated by [commitlint](https://commitlint.js.org/) via a Husky `commit-msg` hook.