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

t = int(input())
ans = []
for i in range(t):
    n = int(input())
    a = list(map(int, input().split()))
    if max(a) == min(a):
        ans.append(-1)
    else:
        s = 0
        m = max(a)
        now = a[0] == m
        for j in range(len(a)):
            if (a[j] == m) != now:
                if a[j] == m:
                    ans.append(j + 1)
                else:
                    ans.append(j)
                break
for x in ans:
    print(x)
