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

__author__ = 'Devesh Bajpai'

'''
https://codeforces.com/problemset/problem/1433/C

Solution: 
'''


def solve(n, arr):

    max_pir = max(arr)

    for i in xrange(0, n):

        if arr[i] != max_pir:
            continue

        if i > 0 and arr[i-1] != max_pir:
            return i+1
        elif i < n-1 and arr[i+1] != max_pir:
            return i+1

    return -1


if __name__ == "__main__":

    t = int(raw_input())

    for _ in xrange(0, t):
        n = int(raw_input())
        arr = map(int, raw_input().split(" "))
        print solve(n, arr)
