After creating a custom configuration for my module "module_name.settings.yml" simpletest fails with this message:

InvalidArgumentException: Invalid database prefix: in Drupal\Core\Test\TestDatabase->__construct() (line 81 of /path/to/installation/core/lib/Drupal/Core/Test/TestDatabase.php)

I reinstalled my module and everything works. I load the configuration with the following code.

$config = \Drupal::config('module_name.settings');
$base = $config->get('module_name.variable');

Still, I can't run my tests. If I remove the content from my configuration, tests run again. I'm using Drupal 8.3.4, Apache 2.4.18, PHP 7.0.8, and MariaDB 10.1.25.

  • What modules are listed for installing? I would bet a million dollars it is because one of the modules is missing a .schema.yml file under the config/schema dir.
    – Kevin
    Jul 28, 2017 at 18:37
  • @Kevin I don't think so, I can install my module. And if I remove the config file run tests properly. Jul 28, 2017 at 18:58
  • Exactly. Because you removed the config file. I ran into the exact same thing earlier this year and patched Menu Breadcrumb to fix the error. Other modules missing a schema.yml file were also patched to fix this error. The error above is very misleading because it is not specific.
    – Kevin
    Jul 28, 2017 at 19:07
  • 1
    @Kevin I think I own you a billion dollars now, you was right. A .schema.yml file was missing. Thanks for your time. Jul 28, 2017 at 19:57

1 Answer 1


Since your module provides a settings.yml file, it must also provide a mymodule.schema.yml file describing the config object that stores the settings.

The real error pertains to something along these lines, and not a database error:

The test did not complete due to a fatal error.
Exception Uncaught e ConfigSchemaCheck   86 Drupal\Core\Config\Testing\ConfigSc
    Drupal\Core\Config\Schema\SchemaIncompleteException: No schema for
    MODULENAME.settings in
    Drupal\Core\Config\Testing\ConfigSchemaChecker->onConfigSave() (line 86

By providing a schema.yml file, clearing cache and re-running the tests this should resolve itself.


You have to be careful of this one, because any contrib module that provides a settings.yml without a matching schema will throw the same error. It is confusing because you can install the module in your main application, but when you install it with a test, it will error out.

It will be easy to narrow down which ones, because it will be one that is listed in your required modules var (protected static $modules = [...]) which is how I stumbled upon the Menu Breadcrumb issue I mentioned.

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