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

def mi():
    return map(int, input().split())
'''
4
4
1 -2 3 -4
3
0 0 0
5
1 -1 1 -1 1
6
40 -31 -9 0 13 -40
'''
for _ in range(int(input())):
    n = int(input())
    a = list(mi())
    ma = max(a)
    mii = min(a)
    if mii==ma:
        print (-1)
        continue
    for i in range(n):
        if a[i]==ma:
            if (i>0 and a[i-1]<ma) or (i<n-1 and a[i+1]<ma):
                print (i+1)
                break
