In https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/Wikibase/+/441203
cache/integration-tests is added as a require-dev dependency of Wikibase
https://integration.wikimedia.org/ci/job/wmf-quibble-vendor-mysql-hhvm-docker/1117/consoleFull shows that cache/integration-tests is installed
but then it is not loaded because "git clean -xqdf" is run because composer test.
The git clean is run from this line https://github.com/wikimedia/integration-quibble/blob/a6791dc60810103f1cf961b62729d29e1e227865/quibble/test.py#L93
This can be expected as without this cleanup the tests would be run with duplicate copies of various libraries potentially at different versions.
It looks like T112895 is slightly related to this
**Possible solutions**
# Don't do the git clean, but this would be bad due to the duplicate library situation described above
# Add the library to the mediawiki require-dev, but this is evil as mediawiki won't actually use it.
# Hardcode the install of the library somewhere in CI, but this is evail as the required version would be fixed for all jobs etc and the require-dev of the extension would not actually be respected
# Some evil hack thing like: https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/Wikibase/+/445190/
# Fix this properly in quibble to use composer-merge-plugin to pull in require-dev dependencies, which won't work due to conflicting dev deps
# Move the thing into core so that #2 isn't evil