Do you tip for a makeup trial?

Yes. Any service, even if it's a trial, expect to tip unless it goes horribly wrong and they had control over the problems. Don't penalize the service provider if you had to tweak things or hash things out. I would only withhold a tip if they were rude/unprofessional/etc...and 20% is the norm.

Yes, you should always tip for a makeup trial. Between 15-20% is standard.

I did. However, I tipped $20 for each of my hair and makeup trials (make up was $125, hair was $100).

Not a trial, but I had my hair and makeup (only eyes due to COVID) done for my engagement session. The total was around $70 and I tipped $10.

Yes, a tip should always be given with a service is provided. I tipped 20% at my hair/make up trial.