# `testing.FakeSession.rulers`

> Contract 2.0.0 · package sha256 `a857eca95b35921109faf997094bb4192f12527d9d0fcd4be7e97f06425bad6e` · generated from `testing.d.ts` by `services/onsite-scripter/scripts/build-contract-docs.mjs`; edit the source, not this file.

Method of [`testing.FakeSession`](testing.FakeSession.md) · labs, `@experimental` · since 2.0.0 · optional: reach it through `has()`

```ts
rulers?(): ReadonlyArray<{
  readonly axis: 'width' | 'height' | 'depth';
  readonly metres: number;
  readonly label: string;
  readonly part: Part | null;
}>;
```

The rulers [`overlays.dimensions`](Overlays.dimensions.md) shows now, as the shopper reads them, so a planner's test
asserts its labels, its per-module split and that they follow its writes: one entry per
ruler, in set order (one set for `per: 'all'`, else one per matched part or model, in
document order) and each set's `axes` order. A `dimensions` call shows at the next drawn
frame, and the rulers are measured again at each drawn frame from current bounds, so after
a write, an undo or a redo they follow at the next `frame()` or `tick(16)`. Empty before
that frame, after `dimensions(null)`, while nothing it matched is visible, and after
[`destroy()`](Session.destroy.md); it never throws and records nothing.
Experimental, so optional in this declaration: a test calls `fake.rulers?.()`.

**Default:** [] (no rulers shown)

## Example

Imports: values (`has`, `validate`, the `Holo*Error` classes, the pure helpers) from `@holostep-configurators/runtime-client`, types from `@holostep-configurators/runtime-client/contract`, `/math` and `/testing` names from those entries; `boot` from the runtime module the root's `loadRuntimeAtFloor` resolves to. A type your page defines is your app's: declare it there, never import it from the package.

Compiled under the contract's strict settings (`examples/declaration/24-FakeSession.rulers.ts`):

```ts
import { createFakeSession } from '@holostep-configurators/runtime-client/testing';
import type { Session } from '@holostep-configurators/runtime-client/contract';
declare const session: Session;
declare const signal: AbortSignal;
// A kitchen planner labels its run of base cabinets in millimetres.
const box = (width: number) => ({
  nodes: [{
    name: 'Carcass',
    mesh: true,
    bounds: { min: { x: 0, y: 0, z: -0.29 }, max: { x: width, y: 0.85, z: 0.29 } },
  }],
});
const at = (nodeId: string, glbUrl: string, x: number) => ({
  nodeId, type: 'ModelNode' as const, enabled: true, glbUrl,
  position: { x, y: 0, z: 0 }, rotation: { x: 0, y: 0, z: 0 }, scale: { x: 1, y: 1, z: 1 },
});
const fake = createFakeSession({
  models: { 'b60.glb': box(0.6), 'b30.glb': box(0.3) },
  root: [at('sink', 'b60.glb', 0), at('drawers', 'b30.glb', 0.6)],
});
let loaded = false;
void fake.idle().then(() => (loaded = true));
for (let i = 0; i < 100 && !loaded; i++) {
  fake.tick(16);
  await new Promise((resolve) => setTimeout(resolve, 0));
}
fake.overlays.dimensions(
  { role: 'product' },
  { per: 'node', axes: ['width'], format: { unit: 'mm' } },
);
fake.frame();                                              // the rulers draw
export const labels = (fake.rulers?.() ?? []).map((r) => `${r.part?.node}: ${r.label}`);
if (labels.join(', ') !== 'sink: 600 mm, drawers: 300 mm') {
  throw new Error('the per-module rulers did not read as planned');
}
```

## Generic-API test (spec 3.1)

| Rule | Result |
| --- | --- |
| 1. Neutral name | pass: `rulers` names no product |
| 2. A precedent | not recorded: no ledger row (coverage.json) names this member or its owner |
| 3. Two apps, or labs | labs (`@experimental` at a stable path, reached through `has()` or `supports()`): it graduates when a second app uses it |
| 4. The cheaper fix first | not recorded per member (Appendix B decides it per need) |