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

t = int(input())
for _ in range(t):
    n = int(input())
    a = list(map(int,input().split()))
    m = max(a)
    flag = 0
    for i in a:
        if i != m:
            flag = 1
            break
    if flag == 0:
        print(-1)
    else:
        for i in range(n):
            if a[i] == m:
                if i>0 and a[i-1] != m:
                    print(i+1)
                    break
                elif i<n-1 and a[i+1] != m:
                    print(i+1)
                    break