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 _ in  range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    if n==a.count(a[0]):
        print(-1)
        continue
    ans=0
    for i in range(n):
        if a[i]>=a[ans]:
            ans=i
    if ans==n-1:
        mx=a[ans]
        while a and a[-1]==mx:
            a.pop()
        if a.count(mx)==0:
            ans=len(a)
        for i in range(len(a)):
            if a[i]==mx:
                ans=i
        
    print(ans+1)