Setup Install a theme for testing, which forces every icon to be a folder: git clone git@github.com:Peterburnett/MDL-70106-tester.git theme/boosticonsbroken Login as admin. Perform the upgrade to install the cloned broken theme. Access to "Site administration / Appearance / Themes / Theme selector" and set the site Default theme to 'Boosticonsbroken'. Go to "Appearance / Themes / Theme settings" and set 'allowcoursethemes' on. Create a test course, and set the 'Force theme' control in the appearance tab to 'Boost'.   Testing instructions Go to "Site administration / Development / Purge caches" and purge caches. Verify the status of the localstorage cache (Firefox instructions): Open the browser devtools using F12 Click the storage tab, expand the 'Local Storage' Menu item, and click the test server domain. In the 'Filter items' bar, enter 'iconmap'. Confirm that the 'iconmap' entry key contains the theme for the iconmap: core_iconsystem/theme/boosticonsbroken/iconmap-fontawesome Access to the course and enable editing mode. Verify that icons that are loaded by JS, such as the move handles on activities, appear correctly (so they are not a folder icon). Open the browser localstorage menu and verify that there are now two iconmaps in the localstorage cache, one for boosticonsbroken and another for boost, that contains the correct mappings.