Answers for "laravel routes controller not found"

Class 'App\Http\Controllers\Admin\Route' not found

use Illuminate\Routing\Route;

laravel route target class not found

Routing namespaces have been updated on Laravel 8.X

On your router, you should define:
use App\Http\Controllers\TestController;

And then, declare:
Route::get('test',[TestController::class, 'test']);