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

for i in range(int(input())):
    n=int(input())
    p = list(input().split())
    if len(p)==p.count(p[0]):
        print(-1)
    else:
        nl=[]
        for item in p:
            nl.append(int(item))
        b=max(nl)
        midx = nl.index(b)
        if midx==0:
            i = 0
            while(True):
                if nl[i]!=b:
                    midx=i-1
                    break
                i+=1
        print(midx+1)