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

tsts = int(input())
for tst in range(tsts):
    ln = int(input())
    prns = list(map(int, input().split(" ")))
    big = max(prns)
    dom = -1
    if prns[0]!=big:
        for i in range(ln):
            if prns[i]==big:
                dom = i+1
                break
    else:
        for j in range(ln):
            if prns[j]!=big:
                dom = j
                break
    print(dom)
