test: add empty fallback coverage for ShareButtons

components/ShareButtons.empty-fallback.test.tsx

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+import { render, screen } from '@testing-library/react';
+import '@testing-library/jest-dom';
+import { describe, it, expect } from 'vitest';
+import ShareButtons from './ShareButtons';
+
+describe('ShareButtons - Empty/Fallback Safety Tests', () => {
+  // Test 1: Minimal Valid Render
+  it('renders successfully with only the required url prop', () => {
+    const { container } = render(<ShareButtons url="https://example.com" />);
+
+    const links = screen.getAllByRole('link');
+    expect(links).toHaveLength(2);
+    expect(screen.getByRole('link', { name: /share on linkedin/i })).toBeInTheDocument();
+    expect(screen.getByRole('link', { name: /share on x \/ twitter/i })).toBeInTheDocument();
+    expect(container.querySelector('svg')).toBeInTheDocument();
+  });
+
+  // Test 2: Missing Optional Inputs
+  it('handles omitted optional title prop gracefully', () => {
+    render(<ShareButtons url="https://example.com" />);
+
+    const twitter = screen.getByRole('link', { name: /share on x \/ twitter/i });
+    expect(twitter).toHaveAttribute(
+      'href',
+      'https://x.com/intent/tweet?url=https%3A%2F%2Fexample.com'
+    );
+    expect(twitter.getAttribute('href')).not.toContain('&text=');
+
+    // All links still render
+    expect(screen.getByRole('link', { name: /share on linkedin/i })).toBeInTheDocument();
+  });
+
+  // Test 3: Empty Values Handling
+  it('renders without crashing when url is an empty string', () => {
+    expect(() => render(<ShareButtons url="" />)).not.toThrow();
+
+    const links = screen.getAllByRole('link');
+    expect(links).toHaveLength(2);
+
+    // LinkedIn URL with empty encoded string
+    const linkedin = screen.getByRole('link', { name: /share on linkedin/i });
+    expect(linkedin).toHaveAttribute(
+      'href',
+      'https://www.linkedin.com/sharing/share-offsite/?url='
+    );
+  });
+
+  // Test 4: Null and Undefined Inputs
+  it('handles undefined title via default parameter without errors', () => {
+    const props: { url: string; title?: string } = {
+      url: 'https://example.com',
+    };
+
+    expect(() => render(<ShareButtons url={props.url} />)).not.toThrow();
+
+    const twitter = screen.getByRole('link', { name: /share on x \/ twitter/i });
+    expect(twitter).toHaveAttribute(
+      'href',
+      'https://x.com/intent/tweet?url=https%3A%2F%2Fexample.com'
+    );
+    expect(twitter.getAttribute('href')).not.toContain('&text=');
+  });
+
+  // Test 5: Structural Integrity Verification
+  it('maintains expected DOM structure in empty-edge state', () => {
+    const { container } = render(<ShareButtons url="https://example.com" />);
+
+    // Root div with flex classes
+    const rootDiv = container.firstElementChild;
+    expect(rootDiv).toBeInTheDocument();
+    expect(rootDiv?.className).toContain('flex');
+    expect(rootDiv?.className).toContain('gap-3');
+
+    // Both links have correct security attributes
+    const links = screen.getAllByRole('link');
+    links.forEach((link) => {
+      expect(link).toHaveAttribute('target', '_blank');
+      expect(link).toHaveAttribute('rel', 'noopener noreferrer');
+    });
+
+    // SVG icons are rendered within each link
+    const svgIcons = container.querySelectorAll('svg');
+    expect(svgIcons).toHaveLength(2);
+    svgIcons.forEach((icon) => {
+      expect(icon).toHaveAttribute('aria-hidden', 'true');
+    });
+  });
+});