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 i in range(int(input())):
    n=int(input())
    arr=list(map(int,input().split()))
    if len(set(arr))==1:
        print(-1)
    else:
        d=max(arr)
        for j in range(1,n):
            if arr[j]==d and arr[j-1]!=d:
                print(j+1)
                break
            elif arr[j]!=d and arr[j-1]==d:
                print(j)
                break