Inverse of the existing be.visible. Reuses the isVisible helper already in src/asserts/index.ts.

Scope

• New case in src/asserts/index.ts returning !isVisible(el).
• Unit test in src/tests/asserts/.
• Add a row in docs/api/assertions.md.
• Add an element with display: none and data-testid="be-hidden" in examples/twd-test-app/src/pages/Assertions.tsx.
• Example test uses screenDom.getByTestId("be-hidden") + twd.should(el, "be.hidden").

Reference

• be.visible implementation in src/asserts/index.ts.

Acceptance criteria

• npm run test:ci is green.
• Example test runs green in the TWD sidebar of twd-test-app.
• docs/api/assertions.md updated.
• PR includes a sidebar screenshot.

How to contribute

Read CONTRIBUTING.md first. Quick steps for this issue:

1. Fork, clone, create a feature branch: git checkout -b feat/be-hidden-assertion.
2. From the repo root, build the library and sync it to the example apps:

   npm install
   npm run build
   npm run copy:mock-sw

3. Install and run the test app:

   cd examples/twd-test-app
   npm install
   npm run dev

4. Open the app in the browser — the TWD sidebar appears on the right. Run your new tests from the sidebar and confirm they pass.
5. Run the library's unit tests from the repo root: npm run test:ci.
6. Open the PR with screenshots of the sidebar showing green tests.

Always prefer screenDom (Testing Library) for element queries. Avoid twd.get() in new code.