Build behaviour on non-default branch

Hi everyone,
the builds are triggered as expected when a change is pushed on a given branch.
What I cannot understand is how the gitlab-ci.yml is picked up.
I have a gitlab-ci.yml on the default branch (development) and another gitlab-ci.yml in a test branch.

I cannot find an explanation of this in the official documentation but it seems to me that only the gitlab-ci.yml on the default branch is considered, is it right? Is this the expected behaviour?
Do i have to delete the gitlab-ci.yml on the non-default branch?

Thanks in advance.
Cheers.