Some of the "unit" tests we have in MediaWiki require things like databases to be set up and data imported. That's not a unit test.
Those are still valuable tests (probably) they just shouldn't be run during our unittest run (which should be as fast as possible).
Related: T89432: Make PHPUnit tests run without installing MediaWiki.
Some limited interaction with the database is appropriate, but only for testing the Database class itself I guess.
If/when that module becomes its own library, we can take it for granted within MediaWiki. At which point we shouldn't need any database in MediaWiki unit tests at all. Instead, we'd mock value objects not the underlying database.
Change 513106 had a related patch set uploaded (by TK-999; owner: TK-999):
[mediawiki/core@master] [WIP/PoC]: Separate MediaWiki unit and integration tests
Change 513106 merged by Jforrester:
[mediawiki/core@master] Separate MediaWiki unit and integration tests
Change 517550 had a related patch set uploaded (by TK-999; owner: TK-999):
[mediawiki/core@master] Introduce separate unit tests PHPUnit configuration
Change 517550 merged by jenkins-bot:
[mediawiki/core@master] Introduce separate unit tests PHPUnit configuration
Change 517701 had a related patch set uploaded (by TK-999; owner: TK-999):
[mediawiki/core@master] Move trivially compatible tests to the unit tests suite
Change 519165 had a related patch set uploaded (by Kosta Harlan; owner: Kosta Harlan):
[mediawiki/core@master] Unit tests: prevent access to global functions and variables
Change 519165 merged by jenkins-bot:
[mediawiki/core@master] Define unit and integration test suites
Change 517701 merged by jenkins-bot:
[mediawiki/core@master] Move trivially compatible tests to the unit tests suite
Didn't know this task existed
I've been working to switch core tests from integration to unit where possible, open patches at https://gerrit.wikimedia.org/r/q/topic:%22unit-tests%22+status:open