Break KernelTestBase dependency on Simpletest, deprecate stub BC traits

Nice catch! Thank you for opening up this issue @Mile23! We are getting somewhere, one day :)

Re-rolled.

Run retest for 8.6.x

@mile23 ok, i only want process it after deploy new drupal core version.
And i think it's not good process to set RTBC after deploy 8.6.x without test

+++ b/core/modules/simpletest/src/AssertContentTrait.php
@@ -2,1495 +2,16 @@
+ *
+ * @deprecated in Drupal 8.5.0, to be removed before Drupal 9.0.0. Use
+ *   Drupal\KernelTests\AssertContentTrait instead.

+++ b/core/modules/simpletest/src/TestServiceProvider.php
@@ -2,54 +2,14 @@
+ * @deprecated in 8.5.0 for removal before Drupal 9.0.0. Use
+ *   Drupal\KernelTests\TestServiceProvider instead.

These should have @see's to the change record to follow our policy. We can't add @trigger_error though because we're still using Simpletest tests.

Also in TestServiceProvider (now not part of Simpletest) we still have code referring to Simpletest and its namespace. I.e:

  /**
   * Add the on demand rebuild route provider service.
   *
   * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container
   */
  public static function addRouteProvider(ContainerBuilder $container) {
    foreach (['router.route_provider' => 'RouteProvider'] as $original_id => $class) {
      // While $container->get() does a recursive resolve, getDefinition() does
      // not, so do it ourselves.
      // @todo Make the code more readable in
      //   https://www.drupal.org/node/2911498.
      for ($id = $original_id; $container->hasAlias($id); $id = (string) $container->getAlias($id)) {
      }
      $definition = $container->getDefinition($id);
      $definition->clearTag('needs_destruction');
      $container->setDefinition("simpletest.$original_id", $definition);
      $container->setDefinition($id, new Definition('Drupal\simpletest\\' . $class));
    }
  }

So we need to do something about \Drupal\simpletest\RouteProvider which has it's own @todo to move out of simpletest linking to #2672762: Move core/modules/simpletest/src/RouteProvider.php to the Drupal\Tests namespace/folder

1. +++ b/core/modules/simpletest/src/RouteProvider.php
   @@ -2,111 +2,15 @@
   diff --git a/core/modules/simpletest/src/TestServiceProvider.php b/core/modules/simpletest/src/TestServiceProvider.php
   
   diff --git a/core/modules/simpletest/src/TestServiceProvider.php b/core/modules/simpletest/src/TestServiceProvider.php
   index 0097803dee..151260c59d 100644
   
   index 0097803dee..151260c59d 100644
   --- a/core/modules/simpletest/src/TestServiceProvider.php
   
   --- a/core/modules/simpletest/src/TestServiceProvider.php
   +++ b/core/modules/simpletest/src/TestServiceProvider.php
   
   +++ b/core/modules/simpletest/src/TestServiceProvider.php
   +++ b/core/modules/simpletest/src/TestServiceProvider.php
   @@ -2,54 +2,16 @@
   
   @@ -2,54 +2,16 @@
    
    namespace Drupal\simpletest;
    
   ...
   +use Drupal\KernelTests\TestServiceProvider as CoreTestServiceProvider;
   +
   +/**
   + * Provides special routing services for tests.
   + *
   + * @deprecated in 8.6.0 for removal before Drupal 9.0.0. Use
   + *   Drupal\KernelTests\TestServiceProvider instead.
   + *
   + * @see https://www.drupal.org/node/2943146
   + */
   +class TestServiceProvider extends CoreTestServiceProvider {
    
    }
   

   I doubt we treat them as real APIs, but sure, let's not overthink this.

2. +++ b/core/tests/Drupal/KernelTests/TestServiceProvider.php
   @@ -38,18 +41,17 @@ public function alter(ContainerBuilder $container) {
      public static function addRouteProvider(ContainerBuilder $container) {
   -    foreach (['router.route_provider' => 'RouteProvider'] as $original_id => $class) {
   -      // While $container->get() does a recursive resolve, getDefinition() does
   -      // not, so do it ourselves.
   -      // @todo Make the code more readable in
   -      //   https://www.drupal.org/node/2911498.
   -      for ($id = $original_id; $container->hasAlias($id); $id = (string) $container->getAlias($id)) {
   -      }
   -      $definition = $container->getDefinition($id);
   -      $definition->clearTag('needs_destruction');
   -      $container->setDefinition("simpletest.$original_id", $definition);
   -      $container->setDefinition($id, new Definition('Drupal\simpletest\\' . $class));
   +    $route_provider_service_name = 'router.route_provider';
   +    // While $container->get() does a recursive resolve, getDefinition() does
   +    // not, so do it ourselves.
   +    // @todo Make the code more readable in
   +    //   https://www.drupal.org/node/2911498.
   +    for ($id = $route_provider_service_name; $container->hasAlias($id); $id = (string) $container->getAlias($id)) {
        }
   +    $definition = $container->getDefinition($id);
   +    $definition->clearTag('needs_destruction');
   +    $container->setDefinition("simpletest.$route_provider_service_name", $definition);
   +    $container->setDefinition($id, new Definition(RouteProvider::class));
   

   Thank you for making this code more readable!

Committed 0858e93 and pushed to 8.6.x. Thanks!