PHPUnit functional test error: No schema for module_filter.settings

The module has defined a config setting called tabs: true. However, there is no associated schema present for the same.

Due to the above reason, any PHPUnit test that is trying to enable the module is failing with the error Drupal\Core\Config\Schema\SchemaIncompleteException: No schema for module_filter.settings

The above error is coming because of https://www.drupal.org/node/2391795

As a workaround, I had to add this property in my test class but it's not the recommended way.

protected $strictConfigSchema = FALSE;

Hence it's best that we fix the problem at the core.