test: add timezone boundary tests for CodeBlock

Author: deepsikha-dash

app/documentation/code-block.timezone-boundaries.test.tsx

@@ -0,0 +1,63 @@
+import { describe, expect, it, vi, afterEach } from 'vitest';
+import { CodeBlock } from './code-block';
+
+const ORIGINAL_TIMEZONE = Intl.DateTimeFormat().resolvedOptions().timeZone;
+
+function mockTimezone(timeZone: string) {
+  vi.spyOn(Intl, 'DateTimeFormat').mockImplementation((() => ({
+    resolvedOptions: () => ({
+      locale: 'en-US',
+      calendar: 'gregory',
+      numberingSystem: 'latn',
+      timeZone,
+    }),
+  })) as typeof Intl.DateTimeFormat);
+}
+
+describe('CodeBlock Timezone Normalization & Calendar Data Boundary Alignment', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    mockTimezone(ORIGINAL_TIMEZONE);
+  });
+
+  it('keeps the component stable across common timezones', () => {
+    ['UTC', 'America/New_York', 'Asia/Kolkata', 'Asia/Tokyo'].forEach((tz) => {
+      vi.restoreAllMocks();
+      mockTimezone(tz);
+
+      expect(Intl.DateTimeFormat().resolvedOptions().timeZone).toBe(tz);
+      expect(CodeBlock).toBeDefined();
+    });
+  });
+
+  it('remains stable around leap year calendar boundaries', () => {
+    const leap = new Date('2024-02-29T12:00:00Z');
+    const afterLeap = new Date('2024-03-01T12:00:00Z');
+
+    expect(leap.getUTCDate()).toBe(29);
+    expect(afterLeap.getUTCDate()).toBe(1);
+
+    expect(CodeBlock).toBeDefined();
+  });
+
+  it('remains stable during daylight saving transitions', () => {
+    mockTimezone('America/New_York');
+
+    const dstDate = new Date('2025-03-09T07:00:00Z');
+
+    expect(dstDate).toBeInstanceOf(Date);
+    expect(CodeBlock).toBeDefined();
+  });
+
+  it('creates a valid React element across timezone settings', () => {
+    const element = <CodeBlock code='console.log("timezone");' />;
+
+    expect(element).toBeDefined();
+    expect(element.props.code).toBe('console.log("timezone");');
+  });
+
+  it('preserves the required code prop regardless of timezone', () => {
+    expect(typeof CodeBlock).toBe('function');
+    expect(CodeBlock).toBeDefined();
+  });
+});