Sounds like you are talking about the "colour change" skills, which just change the colour effect of a skill.

Actual scribed skills add a new option on the relevant skill line page, which then has an tooltip which describes the skill.

For example if you use the Elemental Explosion Grimoire and make a new skill that will then appear on your destruction staff skill page.

Ok so when at the altar and adding scripts first of all hovering over each scripts gives a synopsis of what they do



Secondly a panel appears on the left side of the page that populates with the effects as you add the scripts



Other than that I don't believe it is possible to "test" your chosen skill out, hope that helps?

Edit:- Just to add this adds a totally new skill to the skill line ofc

There is this scribing calculator. I'm not sure how recent it is, but you can give it a go,
https://eso-hub.com/en/scribing-simulator?combination=,,,,