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())
    a = list(map(int, input().split()))
    mx = max(a)
    idx = -2
    for i in range(len(a)):
        if(a[i] == mx and ((i > 0 and a[i-1] < a[i]) or (i < len(a)-1 and a[i+1] < a[i]))):
            idx = i
            break
    print(idx + 1)