Right now the CI servers are using some tools installed and maintained using PEAR.
This is about to move to the composer alternative when it exists. For sure some tools will require PEAR if there is not alternative, but when possible, move.
To begin with, this will be tested with phpunit. So steps are:
1) Delete PEAR phpunit completely.
2) Analyze which composer.json to use (Moodle's bundled one or custom for CI one).
3) Analyze the target directory for the "vendor" stuff (Moodle's root or custom directory).
4) Create a script able to install/update the composer stuff automatically.
5) Move phpunit to use the new version installed and maintained via composer.