The canvas is where regressions hurt most. Golden tests and a performance harness are non‑negotiable.

15.1 — Test layers

Layer	Tooling	What it covers
Unit	flutter_test	Pure logic — bitset ops, region indexing, palette state.
Widget	flutter_test	Library cards, palette strip, paywall sheet, settings.
Golden	flutter_test goldens	Canvas renders for fixed artworks at fixed zoom levels.
Integration	integration_test + Patrol	End‑to‑end: open free artwork, colour, sync, sign in.
Performance	Custom harness	Open a 2 000‑region artwork, record frame times, fail CI on regression.
Backend	Vitest / pgTAP	RLS policies, function behaviour, validation rules.

15.2 — Test artworks

Three fixture artworks are checked into the repo: a 50‑region tutorial piece, a 500‑region typical piece, and a 2 000‑region stress piece. All goldens and performance benchmarks reference these.