test: подключить vitest и покрыть утилиты юнит-тестами

src/utils/formatTraffic.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it, vi } from 'vitest';
+import { formatTraffic } from './formatTraffic';
+
+vi.mock('../i18n', () => ({
+  default: { t: (_key: string, fallback: string) => fallback },
+}));
+
+describe('formatTraffic', () => {
+  it('formats terabytes from 1000 GB up', () => {
+    expect(formatTraffic(1000)).toBe('1.0 TB');
+    expect(formatTraffic(2500)).toBe('2.5 TB');
+  });
+
+  it('formats gigabytes from 1 GB up', () => {
+    expect(formatTraffic(1)).toBe('1.0 GB');
+    expect(formatTraffic(999.94)).toBe('999.9 GB');
+  });
+
+  it('formats sub-gigabyte values as megabytes', () => {
+    expect(formatTraffic(0.5)).toBe('512 MB');
+    expect(formatTraffic(0)).toBe('0 MB');
+  });
+});