Imported from equinor/fusion-skills (skills/.experimental/fusion-framework-testing/SKILL.md). Install upstream with npx skills add equinor/fusion-skills --skill fusion-framework-testing. Copyright stays with the author (MIT).

Fusion Framework Testing

When to use

Use when writing or running a Vitest test for a Fusion Framework React app — a hook, component, route, or complete app — or when setting up/troubleshooting the test project itself.

Typical triggers:

• "Write a test for this component / hook / route"
• "Set up vitest.config.ts for this app"
• "Why does this test hang / hit the network / fail to resolve the app?"
• "Should this be a hook test or a component test?"
• "Share seeded fixtures across a test file"
• "Migrate this suite off Testing Library / jsdom"

Implicit triggers:

• A test file imports @equinor/fusion-framework-vitest-plugin-react-app (or its /test, /config sub-paths)
• vitest.config.ts needs Browser Mode, Playwright, or app-file resolution configured
• A test renders a component/hook that reads useAppModule, useFramework, or similar

When not to use

• Seeding module-specific state (a signed-in user, current context, feature flags, HTTP responses) — use fusion-framework-mocking; this skill only covers rendering/running the test
• dev-server.config.ts API mocking/proxying for local ffc app dev — dev-time only, see fusion-developer-app
• Non-Fusion test suites, or backend/service-repo tests

Required inputs

Mandatory

• What is under test: pure function, hook, component, route, or complete app
• Whether the project already has vitest.config.ts configured for this package

Conditional

• Whether the test needs a specific signed-in user, seeded context, or faked HTTP response (then hand off to fusion-framework-mocking for the seeding details)
• Whether several test files need the same fixture defaults

Instructions

Step 1 — Choose the smallest layer for the behavior under test

Fusion test utilities substitute external boundaries only; Vitest still owns the runner, assertions, lifecycle hooks, spies, timers, and coverage.

A component test should not recreate a portal; an app-lifecycle test should not replace every Fusion hook with a JavaScript module mock. See references/getting-started-and-configuration.md for the full layer-choosing table including module/HTTP layers.

Step 2 — Install and configure

pnpm add -D vitest playwright @vitest/browser-playwright vitest-browser-react \
  @equinor/fusion-framework-vitest-plugin-react-app
pnpm exec playwright install chromium

// vitest.config.ts
import { defineProject } from '@equinor/fusion-framework-vitest-plugin-react-app/config';

export default defineProject();

defineProject registers appTestVitePlugin, headless Chromium via Playwright, test-file inclusion (src/**/*.{test,spec}.{ts,tsx}), and lazy-import warmup. See references/getting-started-and-configuration.md to merge overrides, replace defaults, or resolve non-standard app files.

Step 3 — Write the first test

import { expect } from 'vitest';
import { test } from '@equinor/fusion-framework-vitest-plugin-react-app/test';
import { App } from './App';

test('renders the app', async ({ render }) => {
  const screen = await render(<App />);
  await expect.element(screen.getByRole('heading')).toBeVisible();
});

Always await every Fusion render/hook helper (render, renderHook, renderAppComponent, renderAppHook) — module initialization completes before the first render.

Step 4 — Compose fixtures for reuse (when several tests share seeded state)

Extend test (from /test) to seed shared state, or use test.override(...) for one file/suite without creating a new export. See references/fixtures-and-advanced-usage.md for configureApp/configureFusion/mergeEnvConfig, extend-vs-override, and route/app-lifecycle tests.

Step 5 — Diagnose failures

Consult references/troubleshooting.md's symptom table before guessing — most failures trace to an un-awaited render helper, a missing appTestVitePlugin registration, or an HTTP request with no answering middleware.

Step 6 — Choose Browser Mode or an alternative renderer (only if warranted)

Browser Mode (headless Chromium via Playwright) is the default for fidelity, not speed. Only move to happy-dom/jsdom for a component/hook provably independent of real browser behavior — see references/browser-mode-and-migration.md for the tradeoff and the happy-dom wiring.

Step 7 — Migrate an existing suite (when applicable)

See references/browser-mode-and-migration.md for moving an existing @testing-library/react/jsdom suite onto this package.

Expected output

• A test file using the smallest layer that exercises the behavior under test
• vitest.config.ts correctly registering appTestVitePlugin (directly or via defineProject)
• Every Fusion render/hook helper awaited
• Fixture composition (extend/override) used only when reuse across cases/files justifies it
• Module-specific mock seeding delegated to fusion-framework-mocking

Safety & constraints

Never:

• Claim a rendered result is correct without awaiting the render/hook helper first
• Replace a DOM-emulation gap with an untested polyfill or component swap and call the test passing
• Assume an unmatched HTTP request stays offline — an unmatched request reaches the real network
• Invent Vitest/Playwright configuration options not documented in this skill's references

Always:

• Prefer @equinor/fusion-framework-vitest-plugin-react-app/test's test/render for the normal application path; drop to renderAppHook/renderAppComponent/testApp only when the test must supply env/configure/fusion explicitly
• Keep server.warmup.clientFiles aligned with test.include when test files move
• Cite the real export/API used rather than inventing a Fusion-specific test helper