1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class DominantPiranha {				//1433C
	
	public static void main(String[] args) throws NumberFormatException, IOException {
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int t = Integer.parseInt(br.readLine());
		StringBuilder sb = new StringBuilder();
		while (t-- > 0) 
		{
			int n = Integer.parseInt(br.readLine());
			StringTokenizer st = new StringTokenizer(br.readLine() , " ");
			int temp = Integer.parseInt(st.nextToken());
			boolean f = false;
			for(int i = 1; i < n; i++)
			{
				int tt = Integer.parseInt(st.nextToken());
				if(temp > tt)
				{
					sb.append(i).append("\n");
					f = true;
					break;
				}
				else if(temp < tt)
				{
					sb.append(i+1).append("\n");
					f = true;
					break;
				}
			}
			if(!f) sb.append(-1).append("\n");
		}
		System.out.println(sb);
	}
}