Test before publishing in OSM data

There are lots of different ways of rendering OSM data, so "how things will be seen" will depend on which renderer is displaying the data. OSM data will look different depending on whether you're looking at a website (and depend on which one), a phone app (whichever one).

That said, although you can't add test data to OpenStreetMap, there are a few options. It's possible that what you want to do will be considered OK by https://opengeofiction.net/ (though please check with them first). Another option is to set up your own renderer and load some test data into that. The map legend on this map is done that way and the code that looks after that is here. Unfortunately there isn't a test rendering one of OSM's own dev sites that I am aware of.