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())
    a=map(int,raw_input().split(' '))
    amax=max(a)
    if a.count(amax)==n: 
        if n==1: print 1
        else: print -1 
    else:
        if a.index(amax)<>0: print amax+1
        else:
            for i in range(n-1):
                if a[i]>a[i+1]: 
                    print i+1
                    break
                
