Testing Strategy

Vitest is the test runner (no Jest). Tests live in src/__tests__/ alongside the code they test.

In-memory storage stub

Every test needing IStorageAdapter uses a local stub:

function makeStorage() {
  const store: Record<string, string> = {};
  return {
    read: async (key: string) => store[key] ?? null,
    write: async (key: string, value: string) => { store[key] = value; },
    delete: async (key: string) => { delete store[key]; },
    _store: store,
  };
}

Fake timers

SunglassesCore uses setInterval for auto-flush. Use Vitest fake timers:

beforeEach(() => vi.useFakeTimers());
afterEach(() => { vi.clearAllTimers(); vi.useRealTimers(); });

it('flushes on demand', async () => {
  const client = await SunglassesCore.create({ ... });
  client.capture('event');
  await vi.advanceTimersByTimeAsync(100);
  await client.flush();
  expect(adapter.batches.length).toBe(1);
});

warning

Use vi.advanceTimersByTimeAsync(100) — not vi.runAllTimersAsync(), which loops forever on the flush interval.

Testing adapters

import { vi } from 'vitest';
const mockFetch = vi.fn();
global.fetch = mockFetch;
mockFetch.mockResolvedValueOnce({ ok: true, status: 200 });
// call adapter.send(batch) and assert mockFetch was called

Testing middleware

Cover:

• Happy path: event passes through unchanged
• Drop case: return null
• Transform case: properties modified
• Error case: throw → treated as drop, should not propagate