Fix and enable some unit tests which are not running locally or on pipeline builds

[idseefeld]

Prerequisites

This PR fixes: #19909

Run test. Result should be:

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[AndyButland]

Thanks @idseefeld - good catches and will be good to get these tests running again. Must admit I have no idea why those two cases for the slider test weren't running, but I also can see they aren't.

I left a new minor comments really just for clean-up.

[AndyButland]

Thanks @idseefeld - I'll merge this in now when the checks have passed.