All of the MariaDB and MySQL packages are nowadays on Salsa, the Debian Gitlab instance.
The MariaDB Server, Connector and Galera repositories have Salsa CI configured, which means that every commit will get automatic testing, including Lintian tests, build test, test suite run etc.
You see the pipelines in action at:
The preferred way to submit patches to the MariaDB et al packages is via Merge Requests on Salsa, so your commits get the same testing before accepted.
Signing up for an account at Salsa.debian.org
Anybody can sign up for an account at https://signup.salsa.debian.org/
Using Salsa is very easy for anybody who has used Gitlab before, and very much familiar for those who have experience with Github and similar systems.
Once you have an account, just fork the MariaDB repository you are interested in and start hacking on it.
Using Salsa CI
To enable Salsa CI on your own fork/repositories, please go to your own Settings > CI/CD Settings, expand "General pipelines" and under "Custom CI config path" set the value "debian/gitlab-ci.yml" and timeout to "2h".
See the attached screenshot as an example.
Note that your commit might be merged in several branches (e.g. Debian unstable, Debian stable and Ubuntu release X for example). Please avoid making any direct changes to the debian/changelog file. Your commit message subject line will eventually be in the changelog automatically (via git-dch).
For other tips see the https://salsa.debian.org/mariadb-team/mariadb-10.3/raw/master/debian/README.Contributor file in the package sources itself.