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())
    arr=list(map(int,input().split()))
    Max=max(arr)
    if(n==1):
        print(1)
    elif(len(set(arr))==1):
        print(-1)
    else:
        idx=-1
        for i in range(n):
            if(arr[i]==Max):
                if(i+1<n and arr[i]!=arr[i+1]):
                    idx=i+1;
                if(i-1>=0 and arr[i]!=arr[i-1]):
                    idx=i+1;
        if(idx==-1):
            print(-1)
        else:
            print(idx)