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

for _ in range(int(input())):
    n = int(input())
    pir = [int(p) for p in input().split()]
    index = -1
    maxi = max(pir)
    for i in range(n):
        if(i==0):
            if (pir[i] == maxi and pir[i] != pir[i + 1]):
                index = i+1
                break
        elif(i==n-1):
            if (pir[i] == maxi and pir[i] != pir[i - 1]):
                index = i+1
                break
        else:
            if (pir[i] == maxi and (pir[i] != pir[i - 1] or pir[i] != pir[i + 1])):
                index = i + 1
                break

    print(index)