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 t in range(int(input())):
    k = int(input())
    ntc = list(map(int, input().split()))
    max_inp = max(ntc)
    if len(set(ntc)) == 1:
        print(-1)
    elif max(ntc) == ntc[0]:
        if ntc[0] != ntc[1]:
            print(1)
        else:
            for i in range(k):
                if ntc[i] != ntc[0]:
                    print(i)
                    break
    else:
        print(ntc.index(max(ntc)) + 1)