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 ans(a):
    if len(set(a))==1: return -1
    mx = max(a)
    for i in range(len(a)):
        if a[i]==mx:
            if i>0 and a[i-1]!=a[i]: return i+1
            if i<len(a)-1 and a[i]!=a[i+1]: return i+1

for _ in range(int(input())):
    n = int(input())
    a = list(map(int, input().split()))
    print(ans(a))
    
