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())):
    l = int(input())
    x = list(map(int,input().split()))
    var = max(x)
    var1 = min(x)
    x.append(var)
    x.insert(0, var)
    if var == var1:
        print(-1)
    else:
        for a in range(len(x)-2):
            if x[a+1] == var:
                if x[a+2] != var or x[a] != var:
                    print(a+1)
                    break
                    break
