Repository Pattern in KMP: Flow, Stale-While-Revalidate, Testable

Every data-driven app has the same two problems: users see a loading spinner when cached data would be perfectly fine, and they see an error screen when they should be seeing stale-but-useful content. Both problems come from the same gap — a repository that doesn't implement stale-while-revalidate correctly. This episode shows the full implementation from the MyEuroStatApp project: one cold Flow, a sealed Result‹T› with an isStale flag, and five Turbine test cases that verify every emission path. ⏱️ Chapters: 00:00 — Hook: the loading spinner of shame and the offline error wall 01:05 — The domain contract: observe() + refresh(), strict emission protocol 02:10 — Sealed Result‹T›: Loading, Success(isStale), Error — compiler-checked 03:15 — observe() implementation step by step: emit Loading → cache → network 04:20 — The revalidation branch: try/catch, upsert, stale emit → fresh emit 05:25 — Error swallowing: hadCache flag, when to silently suppress network failure 06:30 — flowOn: upstream on IO, downstream on Main — one call, not many 07:35 — DispatcherProvider: why you never reference Dispatchers.IO directly 08:40 — Turbine: awaitItem / awaitComplete / awaitError, no callbacks needed 09:45 — 5 test scenarios: fresh, stale+ok, no cache+ok, no cache+fail, stale+fail 10:50 — The subtle test: stale cache + network failure must NOT emit Error 11:55 — Fake doubles without Mockk: FakeApiService, FakeDao, FakeClock 📦 Project: github.com/RomanTsisyk/MyEuroStatApp Part of the "Kotlin Multiplatform — full course" series built on a real production app. 🔑 Key concepts covered: • Stale-while-revalidate: emit cached data before network, refresh silently in background • sealed Result‹T›: Loading / Success(data, isStale) / Error(AppError) — exhaustive when • flowOn(dispatchers.io): changes upstream context only, downstream stays on Main • DispatcherProvider injection: replaces Dispatchers.IO in tests with TestDispatcher • Turbine library: awaitItem(), awaitComplete(), awaitError() for linear Flow assertions • Error swallowing: network failure is suppressed when stale cache was already emitted • Handwritten fakes instead of Mockk: commonTest compiles for iOS Native, Mockk doesn't • FakeClock.advance(duration): simulate time without Thread.sleep #KotlinMultiplatform #KMP #KotlinCoroutines #AndroidDevelopment #KotlinAndroid #Flow #RepositoryPattern #CleanArchitecture #ComposeMultiplatform #MobileDevelopment