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 answer(x) :
    x = [int(y) for y in x]
    M = max(x)
    
    for i,tup in enumerate(zip(x[:-1],x[1:])) :
        a,b = tup
        
        if a == M and b < M :
            return i
        
        if a < M and b == M :
            return i + 1
    
    return -1
        
        
t = int(input()) 
for _ in range(t) :
    input()
    x = input()
    print(answer(x.split(" ")))