Wikibase is not an appropriate repository for a generic page split tester. This task tracks the effort to move the code from Wikibase to Core and also a few minor improvements:
- A **rename** should be considered. Perhaps PageSplitter / PageSplitterTest? This might remove some ambiguity around whether PageSplitTester is for unit tests or production code but may decrease grep visibility for A/B or split test code.
- Make the **bucket order** either more explicit or irrelevant. I had to carefully note the order used for config patches and calculate the page_random values for that given order.
- Add **documentation and examples** (some of this lives in the tests), clarify what’s the same and what differs from client A/B tests, clarify that bucket assignments are monotonic.
= Acceptance criteria
[] No PageSplitTester / PageSplitTesterTest or PageRandomLookup / PageRandomLookupTest code, configuration, or strings in Wikibase
[] PageSplitTester (or whatever it's now called) exists in Core and can be used by any extension
[] Bucket order specified by the config is as clear and safe as possible
[] Documentation is revised and added where needed