The tests rely on the ability to run Clutter as stand-alone app,
which hasn't been possible for quite a while now. Event handling
was broken long before that, plus tests that need a human to run
them and evaluate the result aren't that useful to begin with.
It would be neat to test our CSS rendering by setting up a stage,
capturing it and comparing it to a reference image. But writing
some code that exercises backgrounds, borders etc. is hardly the
obstacle to make that happen, and not worth carrying around dead
code.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2811>
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