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The android health gate grepped the trace for "AddTransactionScreen",
which occurs in exactly one place: the hierarchy dump, as a resource-id.
That is a debug artifact standing in for a fact the spec already reports,
and it was wrong in both directions. Against the real 8.4MB trace with
hierarchy stripped, the old gate failed a healthy 200-step run; against a
trace carrying the marker on a transition frame without the route ever
being reported, it passed and called it healthy.
It reads extractor_changes.route now, whose values come from SCREENS in
the spec, so the gate and the app agree on what being on a screen means.
routeOf answers null on a frame showing two screens, which is exactly the
frame the marker was matching.
The drift check grows to cover both new names: extract("route") and the
SCREENS key. The fixtures are re-derived keeping the route entry and no
hierarchy at all; the full artifacts and the fixtures give byte-identical
verdicts, which is what proves the coupling is gone.
Script and fixtures move together: either alone leaves the suite red.
sanderling
Autonomous property-based testing for mobile and web apps.
You write rules that must always hold about your app. sanderling explores the app on its own for minutes or hours, performing thousands of taps, swipes, and inputs, and records every step where a rule breaks. No scripted test paths. One TypeScript spec runs against Android, iOS, and web builds of the same app.
import { extract, always } from "@sanderling/spec";
import { defaultActions } from "@sanderling/spec/defaults";
import { noUncaughtExceptions } from "@sanderling/spec/defaults/properties";
const balance = extract("balance", s =>
parseInt(s.ax.find({ testTag: "Balance" })?.text ?? "0", 10));
export const properties = {
noUncaughtExceptions,
balanceNeverNegative: always(() => balance.current >= 0),
};
export const actionsRoot = defaultActions;
Every run produces a trace: one JSON line and one screenshot per step. sanderling replay opens it in a web UI for stepping through actions, screenshots, property timelines, and violations.
Alpha. Android, iOS, and web (Chrome driver only). Full scope in the v0.1.0 roadmap.
Docs
- Introduction: what property-based testing is and how sanderling works
- Case study: Folio: sanderling finding a real bug in a mobile app
- Getting started: install the CLI and run it against Folio
- Spec language reference
- Examples: folio (KMP, Android/iOS/web), folio-web (React + Vite)
- Architecture for contributors
sanderling, a wading bird that probes the shoreline for bugs that lie beneath.
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