test(react-list): lock down ListItem behavior contract

packages/react-components/react-list/library/src/components/List/useList.test.tsx

@@ -0,0 +1,14 @@
+import * as React from 'react';
+import { renderHook } from '@testing-library/react-hooks';
+import type { TabsterDOMAttribute } from '@fluentui/react-tabster';
+import { useList_unstable } from './useList';
+
+describe('useList_unstable', () => {
+  it('applies Tabster navigation to the list', () => {
+    const { result } = renderHook(() =>
+      useList_unstable({ navigationMode: 'items' }, React.createRef<HTMLUListElement>()),
+    );
+
+    expect((result.current.root as Partial<TabsterDOMAttribute>)['data-tabster']).toContain('mover');
+  });
+});

packages/react-components/react-list/library/src/components/ListItem/useListItem.test.tsx

@@ -0,0 +1,34 @@
+import * as React from 'react';
+import { renderHook } from '@testing-library/react-hooks';
+import { Checkbox } from '@fluentui/react-checkbox';
+import type { TabsterDOMAttribute } from '@fluentui/react-tabster';
+import { List } from '../List/List';
+import { useListItem_unstable } from './useListItem';
+
+describe('useListItem_unstable', () => {
+  it('applies Tabster navigation to focusable list items', () => {
+    const { result } = renderHook(() => useListItem_unstable({}, React.createRef()), {
+      wrapper: ({ children }: React.PropsWithChildren) => <List navigationMode="items">{children}</List>,
+    });
+
+    expect((result.current.root as Partial<TabsterDOMAttribute>)['data-tabster']).toContain('mover');
+  });
+
+  it('does not apply arrow navigation to non focusable list items', () => {
+    const { result } = renderHook(() => useListItem_unstable({}, React.createRef()), {
+      wrapper: ({ children }: React.PropsWithChildren) => <List>{children}</List>,
+    });
+
+    expect((result.current.root as Partial<TabsterDOMAttribute>)['data-tabster']).not.toContain('mover');
+  });
+
+  it('uses a Fluent Checkbox for the checkmark', () => {
+    const { result } = renderHook(() => useListItem_unstable({}, React.createRef()), {
+      wrapper: ({ children }: React.PropsWithChildren) => <List selectionMode="single">{children}</List>,
+    });
+
+    // eslint-disable-next-line @typescript-eslint/no-deprecated
+    expect(result.current.components.checkmark).toBe(Checkbox);
+    expect(result.current.checkmark?.tabIndex).toBe(-1);
+  });
+});