When you write a functional test that creates clean drupal environment from scratch
you man face issues with monolog configuration of this sort:
services:
monolog.handler.db_handler:
class: Drupal\monolog\Logger\Handler\DrupalHandler
arguments: ['@logger.dblog', 10, '400']
Which throws the following error:
Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: The service "monolog.handler.db_handler" has a dependency on a non-existent service "logger.dblog".
1) Create an empty functional test by extending BrowserTestBase (this is not mandatory but it is the way I created it).
2) Create a simple test function just to test if it gets picked up and run.
3) Run phpunit test
Possible explanation of why it happens:
Drupal functionl test environment is trying to build a clean drupal installation. One of the processes of doing that is to go to the sites/default/ folder and find all the service descriptions in .yml files for further initialization, but because @logger.dblog should already be initialized it cannot be registered as a dependency. So it looks like for this particular case injecting services using @ parameter is somehow incorrect.
Active
2.2
Code
You should also enable the Database Logging module in your test or change the settings.php file to not include monolog.services.yml when running test (for example by checking that drupal_valid_test_ua() returns false)