offline_cache_sync_test

Test kit for offline_cache_sync.

• FakeClock: a deterministic clock and scheduler. Retry timers fire in advance().
• FakeConnectivity: flip online/offline from a test.
• FakeServer: an in-memory REST-like backend. It has revisions and ETags, honours Idempotency-Key (replay, or a 422 on payload mismatch), detects conflicts, and can script failures (lostBeforeServer, lostAfterApply, unavailable, reject).
• CrashingStore: kills the "process" before or after the commit of a chosen transaction.
• EngineHarness: all of the above, wired together.
• runLocalStoreConformance: the suite every LocalStore adapter must pass.

test('a lost response is not applied twice', () async {
  final h = await EngineHarness.create();
  h.server.seed('1', {'n': 0});
  await h.items.get('1');
  h.server.failNextSends(1, SendFailure.lostAfterApply);
  await h.items.mutate('1', const Increment('n', 1));
  for (var i = 0; i < 10 && h.storedOps.isNotEmpty; i++) {
    await h.advance(const Duration(minutes: 10));
  }
  expect(h.server.valueOf('1'), {'n': 1});
});