Implement testing library (#2)

Co-authored-by: Eric NGUYEN <enguyen@techform.fr>
Reviewed-on: https://git.siklos-chaneru.duckdns.org/Siklos/svg-layout-designer-react/pulls/2

vite.config.ts

@@ -1,7 +1,18 @@
+/// <reference types="vitest" />
+/// <reference types="vite/client" />
+
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 
 // https://vitejs.dev/config/
 export default defineConfig({
-  plugins: [react()]
+  plugins: [react()],
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: './src/test/setup.ts',
+    // you might want to disable it, if you don't have tests that rely on CSS
+    // since parsing CSS is slow
+    css: false
+  }
 });