isAdminRoute example

$this->assertSession()->linkExists('Settings');
    $this->assertSession()->linkExists('Manage fields');
    $this->assertSession()->linkExists('Manage display');
    $this->assertSession()->linkExists('Manage form display');
  }

  /** * Asserts that admin routes are correctly marked as such. */
  public function testAdminRoute() {
    $route = \Drupal::service('router.route_provider')->getRouteByName('entity.entity_test.field_ui_fields');
    $is_admin = \Drupal::service('router.admin_context')->isAdminRoute($route);
    $this->assertTrue($is_admin, 'Admin route correctly marked for "Manage fields" page.');
  }

}

public function __construct(AccountInterface $user, ConfigFactoryInterface $config_factory, EntityTypeManagerInterface $entity_type_manager, AdminContext $admin_context) {
    $this->user = $user;
    $this->configFactory = $config_factory;
    $this->entityTypeManager = $entity_type_manager;
    $this->adminContext = $admin_context;
  }

  /** * {@inheritdoc} */
  public function applies(RouteMatchInterface $route_match) {
    return ($this->entityTypeManager->hasHandler('user_role', 'storage') && $this->user->hasPermission('view the administration theme') && $this->adminContext->isAdminRoute($route_match->getRouteObject()));
  }

  /** * {@inheritdoc} */
  public function determineActiveTheme(RouteMatchInterface $route_match) {
    return $this->configFactory->get('system.theme')->get('admin') ?: NULL;
  }

}

          $path = $this->pathProcessorManager->processInbound(urldecode(rtrim($cloned_request->getPathInfo(), '/')), $cloned_request);
          $attributes = $this->router->match($path);
        }
        catch (ResourceNotFoundException $e) {
          return FALSE;
        }
        catch (AccessDeniedHttpException $e) {
          return FALSE;
        }
        $route_object = $attributes[RouteObjectInterface::ROUTE_OBJECT];
      }
      $result = $this->adminContext->isAdminRoute($route_object);
    }
    return $result;
  }

}

if (parent::applies($definition, $name, $route)) {
      $entity_type_id = substr($definition['type'], strlen('entity:'));
      // If the entity type is dynamic, defer checking to self::convert().       if (str_starts_with($entity_type_id, '{')) {
        return TRUE;
      }
      // As we only want to override EntityConverter for ConfigEntities, find       // out whether the current entity is a ConfigEntity.       $entity_type = $this->entityTypeManager->getDefinition($entity_type_id);
      if ($entity_type->entityClassImplements(ConfigEntityInterface::class)) {
        return $this->adminContext->isAdminRoute($route);
      }
    }
    return FALSE;
  }

}