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()))
    m = a[0]
    arm = 1
    f = False
    for i in range(1,n):
        if a[i] != a[i-1]:
            f = True
        if a[i]>=m:
            if a[i] != a[i-1]:
                m = a[i]
                arm = i+1
            elif i<n-1:
                if a[i] != a[i+1]:
                    m = a[i]
                    arm = i+1
    if f:
        print(arm)
    else:
        print(-1)