Add vitest

vite.config.js

@@ -3,6 +3,19 @@ import { sveltekit } from '@sveltejs/kit/vite';
 const config = {
 	plugins: [sveltekit()],
 	envPrefix: 'MERMAID_',
-	optimizeDeps: { include: ['mermaid'] }
+	optimizeDeps: { include: ['mermaid'] },
+	ssr: {
+		noExternal: ['@macfja/svelte-persistent-store']
+	},
+	test: {
+		environment: 'jsdom',
+		// in-source testing
+		includeSource: ['src/**/*.{js,ts,svelte}'],
+		// setupFiles: ['./src/tests/setup.ts'],
+		coverage: {
+			exclude: ['src/mocks', '.svelte-kit', 'src/**/*.test.ts'],
+			reporter: ['text', 'json', 'html', 'lcov']
+		}
+	}
 };
 export default config;