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 fish(arr):
    if len(set(arr)) == 1:
        return -1
    m = max(arr)
    for i in range(len(arr)):
        if arr[i] == m:
            if i > 0 and arr[i-1] != m or i < len(arr) - 1 and arr[i+1] != m:
                return i + 1
    return -1

import sys

t = int(sys.stdin.readline())
for _ in range(t):
    n = int(sys.stdin.readline())
    arr = [int(a) for a in sys.stdin.readline().split()]
    print (fish(arr))
