I noticed that Wikibase Selenium tests involve a lot of overhead with browser requests related to mwbot, and we could consolidate some of these.
For example, instead of creating a new MWBot every time createItem() is called, which in turn requires logging in and retrieving an edit token, we could create a single bot instance and store this in the class. We'd have to change the style of calling createItem() to do something like const api = new WikibaseApi(); api.createItem() rather than the existing WikibaseApi.createItem() but that doesn't seem too onerous.
We could also create a single WikibaseApi object in a beforeSuite() hook and reference that in all tests rather than creating a fresh one before each test.