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


t = int(input())

for _ in range(t):
    n = int(input())
    parahnas = list(map(int, input().split()))
    indexes = []
    maxi = max(parahnas)
    # print(maxi)
    for i in range(len(parahnas)):
        if parahnas[i] == maxi:
            indexes.append(i)
    # print(indexes)
    index = 0
    if len(indexes) == len(parahnas):
        print(-1)
    else:
        for ind in indexes:
            if ind > 0 and parahnas[ind] != parahnas[ind-1]:
                index = ind + 1
            if ind < n - 1 and parahnas[ind] != parahnas[ind+1]:
                index = ind + 1
        print(index)
