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())
    k = [int(j) for j in input().split()]
    index = -1
    mx = max(k)
    for i in range(n):
        if k[i]!=mx:
            continue
        if i>0 and k[i-1]!=mx:
            index = i+1
        if i<n-1 and k[i+1]!=mx:
            index = i+1
    print(index)