add concurrent pages test

extension/vite.config.mts

@@ -1,4 +1,3 @@
-
 import { fileURLToPath } from 'url';
 import { dirname, resolve } from 'path';
 import { defineConfig } from 'vite';
@@ -7,6 +6,11 @@ import { viteStaticCopy } from 'vite-plugin-static-copy';
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = dirname(__filename);
 
+const defineEnv: Record<string, string> = {};
+if (process.env.TESTING) {
+  defineEnv['import.meta.env.TESTING'] = 'true';
+}
+
 export default defineConfig({
   plugins: [
     viteStaticCopy({
@@ -26,6 +30,7 @@ export default defineConfig({
       ]
     })
   ],
+
   build: {
     lib: {
       entry: resolve(__dirname, 'src/background.ts'),
@@ -35,5 +40,6 @@ export default defineConfig({
     outDir: 'dist',
     emptyOutDir: false,
     minify: false
-  }
+  },
+  define: defineEnv
 });