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().strip().split()))
    m = max(arr)
    for i in range(n):
        if arr[i] == m:
            break
    flag = False
    if i == 0:
        for j in range(1, n):
            if arr[j] != m:
                flag = True
                break
        if j == n-1 and flag == False:
            print(-1)
        else:
            print(j)
    else:
        print(i+1)