Upgrading doctrine/migrations to version 3 (3.0.1) on a Symfony 4.4 project.
Even when following semver a major version upgrade is expected to have backwards compatibility breaks.
Upgrade to Friends of Behat Symfony Extension
Behat has been getting quite a bit of support recently (see: The future of Behat in 2020)
Many of its extensions have been forked by @FriendsOfBehat and updated to better support current PHP versions.
In particular, the Behat/Symfony2Extension has now been updated to support Symfony ^4.4|^5.0.
The FriendsOfBehat/SymfonyExtension now supports auto-wiring and auto-configuring your contexts.
Multiple Entity Managers With Symfony
I wanted to use different database connections when accessing content. My main use case was to have a read-only user (e.g. reading from a read-replica) and a user with write permissions to do inserts.
This is something that both Symfony and Doctrine have supported for some time.