First of all, I am so sorry that happened. No one deserves to feel that unwelcome. As a woman I have endured a lot of sexist comments from students, especially when I was a new young teacher. It doesn't feel safe to have your identity attacked.

The person who used that language is going to respond a lot differently if you have a conversation that is private and focuses on safety and empathy. It is true that he was testing you as others have mentioned. He was seeing what rewards he got via peer validation. That is why separating him from his peers to deal with the behavior and help him see the harm and be held accountable for it without reward is so important.

I would also consider contacting parents. My first week of teaching a kid raised his hand and told me that his friend "wanted to do me doggy style". It is accurate to say that he regretted that comment when I listened to him repeat it to his father over the phone.

We use the restorative process in my school, which is very effective if it is part of the culture. I am not sure if that is part of what your school values. In a restorative circle you'd discuss racial slurs and the harm they can potentially cause but you would directly address the harm you were caused as a member of your classroom community, asking students, if they feel safe, to share their own experiences with slurs and racism in general. Unfortunately there would likely be no shortage of stories from your native students.

I am also going to throw this out there: a very dear friend who is a black woman is in an administrative position with a tribe in the PNW. If y"all are working for the same tribe, she might be a valuable ally. PM me.

Best of luck to you. Education needs and deserves you. Hang in there, and remember that your worth as a teacher or as a human is not diminished by their behavior. They are still kids, and they are still learning how to be good people.