sanderling/docs/manual/spec-language.md

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Spec language reference

Spec language reference

Module structure

A spec is a TypeScript module evaluated by the Go runner each step. It must export properties and actionsRoot on globalThis (the bundler entry point does this automatically via the final two lines):

import { ... } from "@sanderling/spec";

export const properties = { ... };
export const actionsRoot = weighted(...);

(globalThis as { actions?: unknown }).actions = actionsRoot;
(globalThis as { properties?: unknown }).properties = properties;

State

Every extractor callback receives a State:

interface State {
  ax: AccessibilityTree;
  snapshots: Record<string, unknown>;
  lastAction: Action | null;
  logs: readonly LogEntry[];
  exceptions: readonly ExceptionRecord[];
  time: number;   // ms since run start
}

Field	Description
ax	Live UI hierarchy for this step
snapshots	Key-value data pushed by the app SDK (empty if SDK not integrated)
lastAction	The action dispatched in the previous step, or null on the first step
logs	Log entries collected since the previous step
exceptions	Uncaught exceptions or Sanderling.reportError() calls since the previous step
time	Milliseconds elapsed since the run started

Selectors

Selectors are passed to ax.find(), ax.findAll(), and element-scoped .find() / .findAll().

String selectors

Form	Matches
id:<value>	Exact match on resource-id, or element whose resource-id ends with :id/<value> (Android)
text:<value>	Substring match on text content
desc:<value>	Exact match on accessibility description; also matches when description starts with <value>, (iOS merged labels)
descPrefix:<prefix>	Starts-with match on accessibility description
<attr>:<value>	Substring match on any raw attribute by name

Boolean attributes ("true" / "false") use exact match rather than substring.

Object selectors

Pass an object to apply multiple attribute filters with AND semantics:

s.ax.find({ accessibilityText: "LoginScreen" })
s.ax.find({ testTag: "AccountCard", clickable: true })

Every key-value pair must match. Substring and boolean rules apply per attribute.

Known attribute names are typed; you get autocomplete on testTag, text, content-desc, the boolean states (clickable, enabled, focused, checked, selected), and the cross-platform aliases (identifier, accessibilityIdentifier, accessibilityText, accessibilityLabel, label, resource-id, class, elementType, package, placeholderValue, hintText). Boolean state attributes accept a native true / false. Other attribute keys still type-check as a string-valued fallback so raw driver attributes remain reachable.

Path queries

Chains of string selectors separated by > scope each segment to the subtree of the previous match. Path queries are only supported on the tree root (ax.find, ax.findAll), not on element-scoped .find/.findAll.

s.ax.find("id:HomeScreen > descPrefix:account_card:")
s.ax.find("id:LedgerScreen > desc:ledger_balance_display")

Cross-platform aliases

These key aliases are resolved automatically so selectors work across platforms without changes:

Write this	Also checks
content-desc	accessibilityText
accessibilityText	content-desc
label	accessibilityText
accessibilityLabel	accessibilityText
identifier	resource-id
accessibilityIdentifier	resource-id

AccessibilityElement fields

Fields available on every element returned by find / findAll:

Field	Type	Description
id	string	resource-id (Android) or accessibility identifier (iOS)
text	string	Visible text content
desc	string	Accessibility description (content-desc / accessibilityText)
class	string	View class (Android), element type (iOS), or HTML tag (web)
clickable	boolean	Element is interactive
enabled	boolean	Element is enabled
checked	boolean	Checkbox or toggle state
focused	boolean	Element has input focus
selected	boolean	Selection state
bounds	{ left, top, right, bottom }	Bounding box in device pixels
x	number	Center X (derived from bounds)
y	number	Center Y (derived from bounds)
attrs	Record<string, string>	All raw attributes from the driver

Platform notes

Android

• id maps to the Android resource-id (e.g., com.example:id/button). The id:<value> selector matches by suffix after :id/, so id:button matches com.example:id/button.
• desc maps to content-desc.
• class is the Java view class name (e.g., android.widget.TextView).
• attrs contains raw UIAutomator attributes: package, scrollable, checkable, etc.

iOS

• id maps to the accessibilityIdentifier set via .accessibilityIdentifier in SwiftUI/UIKit.
• desc maps to accessibilityText, which Maestro builds by merging accessibilityLabel and the element's value (e.g., "Close, icon description"). The desc:<value> selector handles this by also matching when the description starts with <value>, .
• class is the XCUITest element type (e.g., XCUIElementTypeButton).
• attrs contains raw XCUITest attributes: title, placeholderValue, hasFocus, etc.

Web (Chrome)

• id maps to the HTML id attribute.
• desc is derived from aria-label, alt, or title.
• class is the lowercase HTML tag name (e.g., button, input).
• attrs contains all HTML attributes available to CDP.

KMP (Kotlin Multiplatform)

KMP apps are tested identically to native apps. An Android KMP build uses the Android driver; an iOS KMP build uses the iOS driver. There is no separate KMP driver. The accessibility tree structure reflects the target platform, so the same selector portability rules apply.

Extractors

const loggedIn = extract((s) => !!s.ax.find("id:home-tab-bar"));
loggedIn.current    // T - value from the current step
loggedIn.previous   // T | undefined - value from the previous step, undefined on first step

Extractors are evaluated before properties and action generators. Use .previous to detect transitions between steps.

LTL operators

Function	Meaning
always(f)	f must hold at every step
eventually(f).within(n, unit)	f must hold at some step within n "milliseconds", "seconds", or "steps"
now(f)	f evaluated at the current step (for use inside always/next bodies)
next(f)	f evaluated at the step immediately after the current one

Formula combinators - available on every Formula:

Method	Meaning
.implies(other)	If this holds, other must also hold
.and(other)	Both must hold
.or(other)	At least one must hold
.not()	Negation

Actions

Constructors

Tap({ on: element | string })
InputText({ into: element | string, text: string })
Swipe({ from: element | Point, to: element | Point, durationMillis?: number })
PressKey({ key: Key })
Wait({ durationMillis: number })

Key values: "back", "home", "enter", "tab", "up", "down", "left", "right".

On web, "back" maps to Backspace and "home" is not supported. All other keys work on all platforms.

Built-in generators

Generator	Behaviour
taps	Random tap on a clickable element
swipes	Random swipe gesture
waitOnce	Idles one step
pressKey	Presses a random supported key

actions(generator)

Wraps a callback that returns Action[]. The callback runs each step the generator is eligible.

const doLogin = actions(() => {
  if (loggedIn.current) return [];
  const submit = loginSubmit.current;
  return submit ? [Tap({ on: submit })] : [];
});

weighted(...entries)

Assembles a weighted tree. Each entry is [weight, generator]. Weights are relative within the tree.

export const actionsRoot = weighted(
  [50, doLogin],
  [10, taps],
  [2,  swipes],
);

from(items)

Returns a Sampler<T> that cycles through a fixed list. Use .generate() to pick an item.

const names = from(["Checking", "Savings", "Travel"]);
// inside an actions() callback:
InputText({ into: nameField, text: names.generate() })

Default properties

import { noUncaughtExceptions, noLogcatErrors } from "@sanderling/spec/defaults/properties";

Property	Fails when
noUncaughtExceptions	An uncaught exception or Sanderling.reportError() call is captured
noLogcatErrors	Logcat emits any error-level (E) lines since the previous step