Failing core/config/themedui* tests

[Comandeer]

Are you reporting a feature request or a bug?

Failing tests

Provide detailed reproduction steps (if any)

tests/core/config/themedui and tests/core/config/themedui2 throw:

Uncaught TypeError: Cannot read property 'registered' of undefined
    at b.toAllowedContentRules (ckeditor.js:1270)
    at window.CKEDITOR.window.CKEDITOR.dom.CKEDITOR.filter.allow (ckeditor.js:213)
    at window.CKEDITOR.window.CKEDITOR.dom.CKEDITOR.filter.allow (ckeditor.js:214)
    at window.CKEDITOR.window.CKEDITOR.dom.CKEDITOR.filter.addFeature (ckeditor.js:218)
    at addFeature (ckeditor.js:265)
    at f (ckeditor.js:649)
    at b (ckeditor.js:648)
    at a (ckeditor.js:650)
    at a.<anonymous> (ckeditor.js:655)
    at a.e (ckeditor.js:10)

Other details

• CKEditor version: 4.80 (built version with uploadimage plugin enabled)

[f1ames]

Seems like there is some race condition, or widget plugin is not loaded for some reason. This error is reproducible on sample (build version) with config (same as in test):

config.plugins = 'about,basicstyles,bidi,blockquote,clipboard,colorbutton,colordialog,div,elementspath,enterkey,entities,find,flash,font,format,forms,horizontalrule,image,iframe,indent,justify,link,list,maximize,newpage,pagebreak,pastefromword,pastetext,preview,print,removeformat,resize,toolbar,save,selectall,showblocks,showborders,smiley,sourcearea,specialchar,stylescombo,table,templates,undo,wysiwygarea';

[f1ames]

Looks like it is caused by stylescombo trying to add widget related styles to ACF:

however, the widget plugin is not present. Removing stylescombo from config or adding uploadimage makes everything is loading fine 🤔

[f1ames]

So now, when uploadimage is included by default also its dependencies are included in ckeditor.js (widget plugin).
Even though these two plugins are not used by the editor (considered above config), widget plugin by default registers its custom styles handler - https://github.com/ckeditor/ckeditor-dev/blob/major/plugins/widget/plugin.js?utf8=%E2%9C%93#L3591-L3608. And so when the stylescombo processes the styles from style.js, the custom styles handler for widget type exists and gets executed. However, as there is no plugins widget initiated it fails.