I want to test a custom module, which uses configuration entities, as described in Creating a configuration entity type in Drupal 8. The configuration is during installation of the module populated by multiple entities, as described in this answer.

The module works fine, but when I want to test it, then I receive three (error) messages during installation of the module:

public static $modules = array('example');

If I delete all the yaml files in the directory config/install/, then the test runs through.

The messages:

1. Warning:

Invalid argument supplied for foreach() in _batch_finished() (line 405 of /www/sites/mysite.dev/htdocs/core/includes/batch.inc) #0 /www/sites/mysite.dev/htdocs/core/includes/bootstrap.inc(552): _drupal_error_handler_real(2, 'Invalid argumen...', '/www/sites/hand...', 405, Array) #1 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(405): _drupal_error_handler(2, 'Invalid argumen...', '/www/sites/hand...', 405, Array) #2 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(333): _batch_finished() #3 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(95): _batch_process() #4 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(77): _batch_do() #5 /www/sites/mysite.dev/htdocs/core/modules/system/src/Controller/BatchController.php(55): _batch_page(Object(Symfony\Component\HttpFoundation\Request)) #6 [internal function]: Drupal\system\Controller\BatchController->batchPage(Object(Symfony\Component\HttpFoundation\Request)) #7 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #8 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() #9 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #10 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #11 [internal function]: Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() #12 /www/sites/mysite.dev/vendor/symfony/http-kernel/HttpKernel.php(144): call_user_func_array(Object(Closure), Array) #13 /www/sites/mysite.dev/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #14 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #15 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #16 /www/sites/mysite.dev/htdocs/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #17 /www/sites/mysite.dev/htdocs/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /www/sites/mysite.dev/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/DrupalKernel.php(656): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /www/sites/mysite.dev/htdocs/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #23 {main}.

2. Notice:

Undefined offset: 0 in _simpletest_batch_finished() (line 474 of /www/sites/mysite.dev/htdocs/core/modules/simpletest/simpletest.module) #0 /www/sites/mysite.dev/htdocs/core/includes/bootstrap.inc(552): _drupal_error_handler_real(8, 'Undefined offse...', '/www/sites/hand...', 474, Array) #1 /www/sites/mysite.dev/htdocs/core/modules/simpletest/simpletest.module(474): _drupal_error_handler(8, 'Undefined offse...', '/www/sites/hand...', 474, Array) #2 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(414): _simpletest_batch_finished(false, Array, Array, '1 Sekunde') #3 /www/sites/mysite.dev/htdocs/core/includes/batch.inc(81): _batch_finished() #4 /www/sites/mysite.dev/htdocs/core/modules/system/src/Controller/BatchController.php(55): _batch_page(Object(Symfony\Component\HttpFoundation\Request)) #5 [internal function]: Drupal\system\Controller\BatchController->batchPage(Object(Symfony\Component\HttpFoundation\Request)) #6 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #7 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() #8 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #9 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #10 [internal function]: Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber{closure}() #11 /www/sites/mysite.dev/vendor/symfony/http-kernel/HttpKernel.php(144): call_user_func_array(Object(Closure), Array) #12 /www/sites/mysite.dev/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #13 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #14 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #15 /www/sites/mysite.dev/htdocs/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #16 /www/sites/mysite.dev/htdocs/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #17 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /www/sites/mysite.dev/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/DrupalKernel.php(656): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /www/sites/mysite.dev/htdocs/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #22 {main}.

3. Error:

InvalidArgumentException: Invalid database prefix: in Drupal\Core\Test\TestDatabase->__construct() (Zeile 81 in /www/sites/mysite.dev/htdocs/core/lib/Drupal/Core/Test/TestDatabase.php).

I have published a test module for testing this issue and also a bug on Drupal.org.