Overstepping Boundaries & Undermining Authority

I had a student, who has put almost no effort in all semester, miss a test and, upon return, ask to write the test in "student success". My past experience with student success rooms is that I cannot trust the work that is done there.

I told the student he would be writing it in class (he does not have an IEP). He complained and argued and I repeated myself, then he stormed out of the room to ask the principal for permission. Another teacher was acting principal today since the actual principal and VP were out of the school. This teacher came to my class, and in front the the entire class, insist that he write the test down in the office. I said no several times, told them my reasoning, but the teacher kept insisting, and even referenced Growing Success. I frustratingly expressed my disagreement but finally yielded and handed over the test.

After school, I spoke with my union rep who later contacted the union and, as I thought, it was ultimately up to me where the student wrote the test.

I feel this teacher, who is a tenured teacher, overstepped their boundaries and undermined my authority, all right in front of the entire class. This is the equivalent of one parent saying no, and the other allowing it in opposition to the other. I have had a few experiences like this with tenured teachers.

How should I handle this?