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 = list(map(int, input().split()))
    maximum = 0
    max_index = 0 
    for i in range(n):
        if(a[i] > maximum):
            max_index = i
            maximum = a[i]
    
    
    if(max_index == 0):
        j = 1
        while(a[j] == maximum):
            if(j == n-1):
                max_index = -1
                break
            max_index = j
            j += 1
    if(max_index != -1):
        max_index += 1        
    print(max_index)        



