test(ShareSheet-timezone-boundaries): add timezone normalization and calendar boundary alignment coverage (JhaSourav07#3618)

## Description

Fixes JhaSourav07#2620

- `components/dashboard/ShareSheet.timezone-boundaries.test.tsx` — added
`5` timezone boundary tests: asserting profile URL stability at `UTC`
midnight, verifying correct rendering under `IST (+05:30)` non-integer
offset, confirming no rendering gaps when activity data spans a leap
year `Feb 29`, validating clean rendering across the US DST
spring-forward transition (Mar 10 2024), and asserting username and URL
alignment at `JST (+09:00)` midnight boundary.

## Pillar

- 🛠️ Other (Bug fix, refactoring, docs)

## Checklist before requesting a review:

- I have read the `CONTRIBUTING.md` file.
- I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- I have run `npm run format` and `npm run lint` locally and resolved
all errors.
- My commits follow the Conventional Commits format.
- I have starred the repo.
- I have made sure that i have only one commit to merge in this PR.

Author: JhaSourav07

components/dashboard/ShareSheet.timezone-boundaries.test.tsx

@@ -0,0 +1,132 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import ShareSheet from './ShareSheet';
+import type { DashboardExportData } from '@/types/dashboard';
+
+vi.mock('framer-motion', () => ({
+  motion: {
+    div: ({ children, ...props }: React.HTMLAttributes<HTMLDivElement>) => (
+      <div {...props}>{children}</div>
+    ),
+  },
+  AnimatePresence: ({ children }: { children: React.ReactNode }) => <>{children}</>,
+}));
+
+vi.mock('react-qr-code', () => ({
+  default: ({ value }: { value: string }) => <svg data-testid="qr-code" data-value={value} />,
+}));
+
+vi.mock('@/hooks/useShareActions', () => ({
+  useShareActions: () => ({
+    states: {},
+    handleTwitter: vi.fn(),
+    handleLinkedIn: vi.fn(),
+    handleReddit: vi.fn(),
+    handleDownloadPNG: vi.fn(),
+    handleDownloadWEBP: vi.fn(),
+    handleDownloadSVG: vi.fn(),
+    handleCopyMarkdown: vi.fn(),
+    handleDownloadJSON: vi.fn(),
+    handleNativeShare: vi.fn(),
+  }),
+}));
+
+function makeMockExportData(overrides?: Partial<DashboardExportData>): DashboardExportData {
+  return {
+    stats: { currentStreak: 5, peakStreak: 10, totalContributions: 100 },
+    languages: [],
+    activity: [],
+    ...overrides,
+  };
+}
+
+const defaultProps = {
+  username: 'octocat',
+  isOpen: true,
+  onClose: vi.fn(),
+  exportData: makeMockExportData(),
+};
+
+describe('ShareSheet - Timezone Normalization & Calendar Data Boundary Alignment', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('UTC boundary: profile URL is constructed correctly when system clock is at UTC midnight boundary', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2024-03-15T00:00:00.000Z'));
+
+    render(<ShareSheet {...defaultProps} />);
+
+    const input = screen.getByDisplayValue(/commitpulse\.vercel\.app\/dashboard\/octocat/i);
+    expect(input).toBeTruthy();
+    expect((input as HTMLInputElement).value).toBe(
+      'https://commitpulse.vercel.app/dashboard/octocat'
+    );
+  });
+
+  it('IST offset (+05:30): component renders correctly when system is in IST timezone offset', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2024-06-15T18:30:00.000Z'));
+
+    render(<ShareSheet {...defaultProps} />);
+
+    expect(screen.getByText('octocat')).toBeTruthy();
+    const input = screen.getByDisplayValue(/commitpulse\.vercel\.app\/dashboard\/octocat/i);
+    expect((input as HTMLInputElement).value).toContain('octocat');
+  });
+
+  it('Leap year boundary: component renders without gaps when exportData spans Feb 29 of a leap year', () => {
+    const leapYearActivity = [
+      { date: '2024-02-28', count: 3, intensity: 2 as const },
+      { date: '2024-02-29', count: 7, intensity: 3 as const },
+      { date: '2024-03-01', count: 2, intensity: 1 as const },
+    ];
+
+    render(
+      <ShareSheet
+        {...defaultProps}
+        exportData={makeMockExportData({ activity: leapYearActivity })}
+      />
+    );
+
+    expect(screen.getByText('octocat')).toBeTruthy();
+    expect(screen.getByDisplayValue(/commitpulse\.vercel\.app\/dashboard\/octocat/i)).toBeTruthy();
+  });
+
+  it('DST transition boundary: component renders correctly around US DST spring-forward date (Mar 10 2024)', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2024-03-10T07:00:00.000Z'));
+
+    const dstActivity = [
+      { date: '2024-03-09', count: 5, intensity: 3 as const },
+      { date: '2024-03-10', count: 4, intensity: 2 as const },
+      { date: '2024-03-11', count: 6, intensity: 3 as const },
+    ];
+
+    render(
+      <ShareSheet {...defaultProps} exportData={makeMockExportData({ activity: dstActivity })} />
+    );
+
+    expect(screen.getByText('octocat')).toBeTruthy();
+    const input = screen.getByDisplayValue(/commitpulse\.vercel\.app\/dashboard\/octocat/i);
+    expect(input).toBeTruthy();
+  });
+
+  it('JST offset (+09:00): profile URL and username render stably when clock is at JST day boundary', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2024-08-20T15:00:00.000Z'));
+
+    render(<ShareSheet {...defaultProps} username="jst-user" />);
+
+    expect(screen.getByText('jst-user')).toBeTruthy();
+    const input = screen.getByDisplayValue(/commitpulse\.vercel\.app\/dashboard\/jst-user/i);
+    expect((input as HTMLInputElement).value).toBe(
+      'https://commitpulse.vercel.app/dashboard/jst-user'
+    );
+  });
+});