ha-frontend-testing

name	ha-frontend-testing
description	Home Assistant frontend testing and validation workflow. Use when adding or updating tests, running lint, TypeScript checks, Vitest, Playwright e2e suites, dev servers, or chart-data benchmarks.

HA Frontend Testing

Use this skill when choosing or running validation for frontend changes.

Test Helpers

• Before adding or changing tests, inspect the relevant suite's existing helpers and fixtures. Reuse them instead of duplicating setup, test data, navigation, interactions, waits, or assertions.
• When the same test flow appears more than once, move it into the closest suite-local helper with a focused interface.
• Keep one-off test behaviour in the test unless a helper makes the intent materially clearer. Do not hide the behaviour under test behind broad, configurable abstractions.

Core Commands

yarn lint          # ESLint + Prettier + TypeScript + Lit
yarn format        # Auto-fix ESLint + Prettier
yarn lint:types    # TypeScript compiler, run without file arguments
yarn test          # Vitest
yarn build         # Full production build
yarn dev           # App dev server
yarn dev:serve     # Local serving dev server

Never run tsc or yarn lint:types with file arguments. File arguments make tsc ignore tsconfig.json and can emit .js files into src/.

For focused type feedback on one file, use editor diagnostics instead of a file-scoped tsc command.

Production Builds

Production builds support foreground and managed background execution:

yarn build                         # Full foreground build
yarn build --background            # Full managed background build
yarn build --modern                # Modern frontend_latest bundle only
yarn build --modern --background   # Modern managed background build
yarn build --status
yarn build --logs [--follow]
yarn build --stop

Use yarn build --modern --background for production bundle-size or browser performance comparisons that only need modern browser output. It runs the normal metadata and static preparation, minifies and compresses the modern frontend_latest bundle and shared static assets, and generates modern-only entry pages and service workers. It deliberately skips the legacy bundle and its service worker.

Do not pass --help, --background, or --modern to script/build_frontend; that raw script does not parse arguments and always starts the full foreground build. Use yarn build for managed builds. App builds and development servers keep exclusive ownership of hass_frontend/ for their lifetime.

Managed app, demo, gallery, and E2E app workflows share one lifetime lock, so only one build or development server can run at a time.

When To Add Tests

• Write tests for code that computes something: data processing, utility functions, config validation, and what happens when the user interacts with a component.
• Do not write tests that check what a component looks like: its text, CSS classes, styles, or slots. Do not write tests that check the default value of an option.
• A component that only takes data from contexts and helpers and puts it in a template does not need a test.
• If you are not sure a test is useful, describe the test and what it would catch, and let the user decide.
• Tests never talk to a real Home Assistant. Replace callWS, callApi, and the connection with fakes.

Dev Servers

yarn dev builds and watches the app, served by a running Home Assistant core configured through development_repo.

yarn dev:serve also serves locally and supports -c for the core URL and -p for the port. The default is 8124, or 8123 in a devcontainer.

Dev server commands support --background, --status, --stop, and --logs [--follow]. yarn dev, yarn dev:serve, yarn dev:demo, and yarn dev:gallery also support --fetch-translations; this runs translation fetching, including first-time GitHub device authentication, under the workflow lock before starting the watcher. It works in foreground and background modes. Prefer managed background mode while iterating so the watcher stays available across test runs without occupying the terminal. yarn dev and yarn dev:serve share one managed process slot because both write the app output.

Playwright E2E

Each suite has its own dev server port. Playwright reuses an existing server locally when its configured URL responds; otherwise it performs a slow full build. When a development watcher is being reused, rspack recompiles on save and reruns should not need a restart.

Start the relevant suite server, then run that suite:

Suite	Background server	Test command
App	yarn test:e2e:app:dev --background on 8095	yarn test:e2e:app
Demo	yarn dev:demo --background on 8090	yarn test:e2e:demo
Gallery	yarn dev:gallery --background on 8100	yarn test:e2e:gallery

The custom development wrappers use /__ha_dev_status to identify and manage their own suites. Playwright server reuse checks the configured URL instead. Wrapper start and stop operations are idempotent for a matching suite and reject an unrelated process occupying the port.

Local runs against a watched development server do not always match CI's clean build artifacts, environment, sharding, or worker configuration. Use background servers for the fast iteration loop, but confirm the relevant CI jobs complete successfully before considering E2E changes verified.

Use -g "<title>" --project=chromium to narrow a run. yarn test:e2e runs suites sequentially when managed servers are unavailable to prevent cold builds racing over shared generated assets. Run suites directly; piping through output truncation hides progress and failures.

The app suite uses a stripped-down harness for e2e. Demo and gallery use their normal dev servers.

Benchmarks

For chart data transforms such as history, statistics, energy, and downsampling, read and follow the complete workflow in test/benchmarks/README.md before making benchmark or optimization changes.

That workflow owns the baseline, noise analysis, guardrails, acceptance thresholds, and reporting requirements. In particular, optimizations must keep output bit-identical; never update snapshots or modify fixtures to make an optimization pass.

Verification Selection

• Documentation-only change: no code test required unless examples or commands changed.
• Type-only or utility change: run focused Vitest if available, then yarn lint:types if practical.
• Lit component change: run relevant tests plus lint or typecheck depending on scope.
• E2E-sensitive flow: start the relevant e2e dev server and run the narrow Playwright suite.
• Broad refactor: run yarn lint and relevant test suites when practical.