diff --git a/src/utils/campaign.test.ts b/src/utils/campaign.test.ts
new file mode 100644
index 0000000..c4cfb35
--- /dev/null
+++ b/src/utils/campaign.test.ts
@@ -0,0 +1,91 @@
+import { readFileSync } from 'node:fs';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { consumeCampaignSlug, getPendingCampaignSlug } from './campaign';
+
+const CAMPAIGN_KEY = 'campaign_slug';
+const CAMPAIGN_TTL_KEY = 'campaign_slug_ttl';
+const HOUR = 60 * 60 * 1000;
+
+function fakeLocalStorage(): Storage {
+  const store = new Map<string, string>();
+  return {
+    get length() {
+      return store.size;
+    },
+    clear: () => store.clear(),
+    getItem: (key: string) => store.get(key) ?? null,
+    key: (index: number) => [...store.keys()][index] ?? null,
+    removeItem: (key: string) => void store.delete(key),
+    setItem: (key: string, value: string) => void store.set(key, value),
+  } as Storage;
+}
+
+function storeSlug(slug: string, expiresInMs = 24 * HOUR): void {
+  localStorage.setItem(CAMPAIGN_KEY, slug);
+  localStorage.setItem(CAMPAIGN_TTL_KEY, String(Date.now() + expiresInMs));
+}
+
+beforeEach(() => {
+  vi.stubGlobal('localStorage', fakeLocalStorage());
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+describe('getPendingCampaignSlug', () => {
+  it('returns the stored slug', () => {
+    storeSlug('summer_sale');
+
+    expect(getPendingCampaignSlug()).toBe('summer_sale');
+  });
+
+  // Гостевая покупка на лендинге читает слаг этим геттером. Если он начнёт
+  // очищать хранилище, тот же клиент, зайдя потом в кабинет, потеряет
+  // привязку к кампании — auth-флоу уже ничего не найдёт.
+  it('does not consume the slug', () => {
+    storeSlug('summer_sale');
+
+    getPendingCampaignSlug();
+
+    expect(getPendingCampaignSlug()).toBe('summer_sale');
+    expect(localStorage.getItem(CAMPAIGN_KEY)).toBe('summer_sale');
+  });
+
+  it('drops an expired slug', () => {
+    storeSlug('summer_sale', -HOUR);
+
+    expect(getPendingCampaignSlug()).toBeNull();
+    expect(localStorage.getItem(CAMPAIGN_TTL_KEY)).toBeNull();
+  });
+
+  it('returns null when nothing was captured', () => {
+    expect(getPendingCampaignSlug()).toBeNull();
+  });
+});
+
+describe('consumeCampaignSlug', () => {
+  it('clears the slug after reading it once', () => {
+    storeSlug('summer_sale');
+
+    expect(consumeCampaignSlug()).toBe('summer_sale');
+    expect(consumeCampaignSlug()).toBeNull();
+  });
+});
+
+// Компоненты в этом репозитории не рендерятся в тестах (vitest на node, без
+// jsdom), поэтому отправку слага фиксируем по исходнику: без неё покупка
+// гостем не попадает в статистику кампании и не даёт её бонус.
+describe('QuickPurchase source', () => {
+  const source = readFileSync(new URL('../pages/QuickPurchase.tsx', import.meta.url), 'utf8');
+
+  it('puts the campaign slug into the purchase payload', () => {
+    expect(source).toContain('data.campaign_slug = campaignSlug');
+  });
+
+  it('reads the slug without consuming it', () => {
+    expect(source).toContain('getPendingCampaignSlug()');
+    expect(source).not.toContain('consumeCampaignSlug');
+  });
+});