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 dominantPhirana(aquarium, length):
    max_, index = aquarium[0], 0
    if len(set(aquarium)) == 1:
        print(-1)
        return
    for i in range(1,len(aquarium)):
        if aquarium[i] >= max_ and aquarium[i] > aquarium[i-1]:
            max_, index = aquarium[i], i
    print(index+1)

if __name__ == "__main__":
    testcases = int(input())
    length = int(input())
    aquarium = list(map(int, input().split()))
    while testcases:
        testcases -= 1
        dominantPhirana(aquarium, length)