if in taxonomy – conditional?

I need to test if a custom post is in a custom taxonomy.

I’m not looking for the terms, there are easy ways to get them.

The issue is the taxonomy itself.

What I need is something like if(in_taxonomy('taxonomy-name'))

It’s not like in_category() since category is itself a taxonomy, it’s one level higher so to speak.

I’ve spent hours on this and gotten nowhere. Any suggestions?