Svelte Testing

Svelte Testing

Quick Start

// Client-side component test (.svelte.test.ts)
import { render } from 'vitest-browser-svelte';
import { expect } from 'vitest';
import Button from './button.svelte';

test('button click increments counter', async () => {
	const { page } = render(Button);
	const button = page.getByRole('button', { name: /click me/i });

	await button.click();
	await expect.element(button).toHaveTextContent('Clicked: 1');
});

Core Principles

• Always use locators: page.getBy*() methods, never containers
• Multiple elements: Use .first(), .nth(), .last() to avoid strict mode violations
• Use untrack(): When accessing $derived values in tests
• Real API objects: Test with FormData/Request, minimal mocking

Reference Files

• core-principles | foundation-first | client-examples
• server-ssr-examples | critical-patterns
• client-server-alignment | troubleshooting

Notes

• Never click SvelteKit form submit buttons - Always use await expect.element()
• Test files: .svelte.test.ts (client), .ssr.test.ts (SSR), server.test.ts (API)