In MDL-81698 (various PHPUnit cleanups) it was detected that we had the lib/tests/rtlcss_test.php test file had 3 commented-out tests:

• test_background_image
• test_special
• test_transforms

With comment:

Not supported by MoodleHQ/RTLCSS yet

And, because having commented tests is not good we proceeded to un-comment it and to mark them as skipped, with message:

Not yet supported!

So, this issue is about to:

1. Decide if the tests should be removed or we want to keep them as reference for future development of the RTL generator.
2. Proceed with the decision.

Ciao