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 = 0
    ind = 0
    win = False
    for i in range(n):
        if a[i]>m:
            m = a[i]
            ind = i
        if a[i]!=a[0]:
            win = True
    if not win:
        print(-1)
        continue
    if ind==0 and a[1]==m:
        for i in range(n-1):
            if a[i+1]<m:
                ind = i
                break
    print(ind+1)
