test(Breadcrumb): add test for BreadcrumbHeader component

src/entities/Breadcrumb/ui/BreadcrumbHeader/BreadcrumbHeader.svelte.test.ts

@@ -0,0 +1,11 @@
+import { render } from '@testing-library/svelte';
+import BreadcrumbHeader from './BreadcrumbHeader.svelte';
+
+const context = new Map([['responsive', { isMobile: false, isMobileOrTablet: false }]]);
+
+describe('BreadcrumbHeader', () => {
+    it('renders nothing when no sections have been scrolled past', () => {
+        const { container } = render(BreadcrumbHeader, { context });
+        expect(container.firstElementChild).toBeNull();
+    });
+});