Replace helpers with their class implementation

These helpers are deprecated and will be removed in a future version.

database-testing.md

@@ -78,6 +78,7 @@ It is often useful to reset your database after each test so that data from a pr
 
 When testing, you may need to insert a few records into your database before executing your test. Instead of manually specifying the value of each column when you create this test data, Laravel allows you to define a default set of attributes for each of your [Eloquent models](/docs/{{version}}/eloquent) using model factories. To get started, take a look at the `database/factories/UserFactory.php` file in your application. Out of the box, this file contains one factory definition:
 
+    use Illuminate\Support\Str;
     use Faker\Generator as Faker;
 
     $factory->define(App\User::class, function (Faker $faker) {
@@ -86,7 +87,7 @@ When testing, you may need to insert a few records into your database before exe
             'email' => $faker->unique()->safeEmail,
             'email_verified_at' => now(),
             'password' => '$2y$10$TKh8H1.PfQx37YgCzwiKb.KjNyWgaHb9cbcoQgdIVFlYg7B77UdFm', // secret
-            'remember_token' => str_random(10),
+            'remember_token' => Str::random(10),
         ];
     });