Rails rspec testing mailer is opening letter_opener but not filling mailer deliveries

Every test i'm running that is triggering a mailer is opening letter_opener like if it is in development envrionment. I add a puts Rails.env in the test and the test is telling : test

Letter opener is not even added in the test group in the gemfile. How it can work ? That is not the real problem. The problem is that Mailer Deliveries is not filled at all. The count stay at zero.

I configured my test.rb with

```config.action_mailer.delivery_method = :test````

What do i need to check ?