Overlay.js has already been migrated to webpack's control in T205593, but its associated tests proved to be challenging to migrate due to Overlay's use of `mw.template.get` and it's dependencies use of `mw.template.get` (Anchor.js, Button.js). It was thus decided to leave its test file as is, and migrate it in a future card (this one).
= Acceptance criteria
[] Overlay.test.js is migrated to tests/node-qunit/mobile.startup and can be run from headless qunit
[] `$testFiles[] = 'tests/qunit/mobile.startup/Overlay.test.js;` line is removed from MobileFrontend.hooks.php
Note: Adding additional test coverage is out of scope and will be added separately.
= Sign off steps
[] Measure and record code coverage on [[ https://www.mediawiki.org/wiki/Reading/Web/Projects/Invest_in_the_MobileFrontend_%26_MinervaNeue_frontend_architecture/Progress?useskin=vector | the wiki page ]]