La clase de destino [] no existe.
composer dump-autoload
Illuminate\Contracts \ Container\BindingResolutionException target calss no existe
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']);
Illuminate\Contracts \ Container\BindingResolutionException La clase de destino [SlugController] no existe.
Route::get('/test/{slug}', 'App\Http\Controllers\SlugController@show' );