A minimal Kotlin Multiplatform personal-ledger app: login with demo credentials, create accounts, add credits and debits. Shared UI across Android, iOS, and Web via Compose Multiplatform. Doubles as the example sanderling runs its property-based specs against.

Stack

Kotlin Multiplatform + Compose Multiplatform (shared UI)
kotlinx.serialization for file-backed persistence
kotlinx.coroutines for state flows
sanderling sdk-android for harness integration on Android

Prerequisites

just
JDK 17
Android SDK (auto-discovered under $ANDROID_HOME, ~/Library/Android/sdk, or the Homebrew cask)
Xcode 16+ and xcodegen (brew install xcodegen) for iOS

Android

just install      # build + install on a booted emulator / device
just uninstall
just clean

iOS

just ios                          # default device: iPhone 17 Pro
IOS_DEVICE="iPhone 15" just ios   # pick a different simulator

just ios regenerates iosApp/iosApp.xcodeproj from iosApp/project.yml, builds the KMP framework, links it into the SwiftUI host, installs, and launches.

Demo credentials

email:    [email protected]
password: ledger123

Run a sanderling test (Android)

just test

If no device is connected, sanderling boots the single AVD it finds. With multiple AVDs, pick one:

AVD=Pixel_7 just test

Persistent settings can live in .env alongside the justfile:

AVD=Pixel_7
DURATION=5m

Traces land in ./sanderling/runs/<timestamp>/.

How it connects to sanderling

composeApp/src/androidMain/.../FolioApplication.kt calls Sanderling.start(this) and registers snapshot extractors (logged_in, account_count, total_balance, route)
sanderling/spec.ts imports @sanderling/spec, reads those snapshots, asserts properties, and weights the actions the fuzzer picks from
just test invokes sanderling test against the installed APK