Is there a way to test a plugin without installing Discourse (similar to the theme-creator platform)?
No, there’s no such thing.
You need to have Discourse up and running in order to try a plugin - unless the author of the plugin offers a live demo. That said, you can try plugins on a development install. Check the #dev-install tag for more on that.
Why not just install it and test it. If you dont like it theb Uninstall. Quite easy, I think