chore: refactorings for sidebar handling

tests/renderer/components/SidebarDateFormatting.test.ts

@@ -0,0 +1,54 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { formatSidebarRelativeDate } from '../../../src/renderer/components/Sidebar/sidebarDateFormatting';
+
+describe('formatSidebarRelativeDate', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2026-02-23T12:00:00.000Z'));
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('formats same-day dates as time', () => {
+    const result = formatSidebarRelativeDate({
+      dateString: '2026-02-23T10:30:00.000Z',
+      language: 'en',
+      t: () => 'Yesterday',
+    });
+
+    expect(result).toMatch(/\d/);
+    expect(result).not.toBe('Yesterday');
+  });
+
+  it('formats one-day-old dates as localized yesterday label', () => {
+    const result = formatSidebarRelativeDate({
+      dateString: '2026-02-22T10:30:00.000Z',
+      language: 'en',
+      t: () => 'Yesterday',
+    });
+
+    expect(result).toBe('Yesterday');
+  });
+
+  it('formats older dates within a week using weekday', () => {
+    const result = formatSidebarRelativeDate({
+      dateString: '2026-02-20T10:30:00.000Z',
+      language: 'en',
+      t: () => 'Yesterday',
+    });
+
+    expect(result).toMatch(/^[A-Za-z]{3}$/);
+  });
+
+  it('formats older dates with month/day', () => {
+    const result = formatSidebarRelativeDate({
+      dateString: '2026-02-10T10:30:00.000Z',
+      language: 'en',
+      t: () => 'Yesterday',
+    });
+
+    expect(result).toMatch(/[A-Za-z]{3}/);
+  });
+});