Sinon.JS is ubiquitous in Wikimedia's repositories. However, [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/master/resources/lib/sinonjs/sinon.js#2 | the version used is outdated and now six major versions behind ]]. The consequence is that developers cannot apply best practice and instead proliferates technical debt. Projects such as [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/MobileFrontend/+/master/package.json#57 | MobileFrontend have already begun to deviate ]]. This task encompasses the work to revise the version provided in Core, identify common upgrade failure patterns in Core, skins, and extensions, and open tasks or patches for their resolution.
== AC
[] The latest version of Sinon.JS is usable everywhere.
== QA
[] Previously passing tests still pass.