test: scaffold component testing with Vitest

vite.config.ts

@@ -0,0 +1,22 @@
+/// <reference types="vitest" />
+import { svelte, vitePreprocess } from "@sveltejs/vite-plugin-svelte";
+import { optimizeImports } from "carbon-preprocess-svelte";
+import { defineConfig } from "vite";
+
+export default defineConfig({
+  root: "./tests",
+  plugins: [
+    svelte({
+      preprocess: [vitePreprocess(), optimizeImports()],
+    }),
+  ],
+  optimizeDeps: {
+    exclude: ["carbon-components-svelte", "carbon-icons-svelte"],
+  },
+  resolve: process.env.VITEST ? { conditions: ["browser"] } : undefined,
+  test: {
+    globals: true,
+    environment: "jsdom",
+    setupFiles: ["./tests/setup-tests.ts"],
+  },
+});