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())):
    input()

    x = list(map(int, input().split()))
    # print(x)
    tek = x[0]
    maid = 0
    ravn = False

    for i, v in enumerate(x[1:], 1):
        if tek > v:
            tek += i if ravn else 1
            ravn = False
        elif tek < v:
            tek = v + i
            maid = i
            ravn = False
        else:
            if v == x[i - 1]:
                ravn = True
            else:
                tek += i
            maid = i

    if tek == x[maid]:
        print(-1)
    else:
        print(maid + 1)
