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

def same(a,n):
    c = 0
    for i in range(n-1):
        if a[i] == a[i+1]:
            c += 1
    return False if c == n-1 else True
t = int(input())
while(t):
    t -= 1
    n = int(input())
    a = list(map(int,input().split()))[:n]
    if a == sorted(a) and same(a,n):
        print(n)
    else:
        for i in range(n):
            if i == 0:
                if a[i+1] < a[i]:
                    print(i+1)
                    break
            elif i == n-1:
                if a[i-1] < a[i]:
                    print(i+1)
                    break
                else:
                    print(-1)
                    break
            else:
                if a[i-1] < a[i]:
                    print(i+1)
                    break
                elif a[i+1] < a[i]:
                    print(i+1)
                    break
