Clean install of current 5.3 branch

Install completes successfully

Enable debug in configuration.php and log in to the admin

Class "Joomla\Plugin\SampleData\Testing\Extension\Testing" not found

Call Stack
#	Function	Location
1	()	JROOT\plugins\sampledata\testing\services\provider.php:37
2	Joomla\DI\ServiceProviderInterface@anonymousD:\repos\j51\plugins\sampledata\testing\services\provider.php:22$89bce->{closure}()	JROOT\libraries\vendor\joomla\di\src\ContainerResource.php:172
3	Joomla\DI\ContainerResource->getInstance()	JROOT\libraries\vendor\joomla\di\src\Container.php:95
4	Joomla\DI\Container->get()	JROOT\libraries\src\Extension\ExtensionManagerTrait.php:177
5	Joomla\CMS\Application\CMSApplication->loadExtension()	JROOT\libraries\src\Extension\ExtensionManagerTrait.php:99
6	Joomla\CMS\Application\CMSApplication->bootPlugin()	JROOT\libraries\src\Plugin\PluginHelper.php:232
7	Joomla\CMS\Plugin\PluginHelper::import()	JROOT\libraries\src\Plugin\PluginHelper.php:192
8	Joomla\CMS\Plugin\PluginHelper::importPlugin()	JROOT\administrator\modules\mod_sampledata\src\Helper\SampledataHelper.php:37
9	Joomla\Module\Sampledata\Administrator\Helper\SampledataHelper->getSampledataList()	JROOT\administrator\modules\mod_sampledata\src\Dispatcher\Dispatcher.php:41
10	Joomla\Module\Sampledata\Administrator\Dispatcher\Dispatcher->getLayoutData()	JROOT\libraries\src\Dispatcher\AbstractModuleDispatcher.php:63
11	Joomla\CMS\Dispatcher\AbstractModuleDispatcher->dispatch()	JROOT\libraries\src\Helper\ModuleHelper.php:289
12	Joomla\CMS\Helper\ModuleHelper::renderRawModule()	JROOT\libraries\src\Helper\ModuleHelper.php:160
13	Joomla\CMS\Helper\ModuleHelper::renderModule()	JROOT\administrator\components\com_cpanel\tmpl\cpanel\default.php:57
14	include()	JROOT\libraries\src\MVC\View\HtmlView.php:416
15	Joomla\CMS\MVC\View\HtmlView->loadTemplate()	JROOT\libraries\src\MVC\View\HtmlView.php:204
16	Joomla\CMS\MVC\View\HtmlView->display()	JROOT\administrator\components\com_cpanel\src\View\Cpanel\HtmlView.php:157
17	Joomla\Component\Cpanel\Administrator\View\Cpanel\HtmlView->display()	JROOT\libraries\src\MVC\Controller\BaseController.php:697
18	Joomla\CMS\MVC\Controller\BaseController->display()	JROOT\administrator\components\com_cpanel\src\Controller\DisplayController.php:57
19	Joomla\Component\Cpanel\Administrator\Controller\DisplayController->display()	JROOT\libraries\src\MVC\Controller\BaseController.php:730
20	Joomla\CMS\MVC\Controller\BaseController->execute()	JROOT\libraries\src\Dispatcher\ComponentDispatcher.php:143
21	Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()	JROOT\libraries\src\Component\ComponentHelper.php:361
22	Joomla\CMS\Component\ComponentHelper::renderComponent()	JROOT\libraries\src\Application\AdministratorApplication.php:150
23	Joomla\CMS\Application\AdministratorApplication->dispatch()	JROOT\libraries\src\Application\AdministratorApplication.php:205
24	Joomla\CMS\Application\AdministratorApplication->doExecute()	JROOT\libraries\src\Application\CMSApplication.php:306
25	Joomla\CMS\Application\CMSApplication->execute()	JROOT\administrator\includes\app.php:58
26	require_once()	JROOT\administrator\index.php:32