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 pyranha(n, a):
    counter = 0
    for i in range(n-1):
        if a[i] == a[i + 1]:
            counter += 1
            if counter == n-1:
                return(-1)                           
    else:
        maximus = max(a)
        for i in range(len(a)):
            if a[i] == maximus and i != 0:
                return(i+1)                
            elif a[i] == maximus and i == 0:
                for j in range(len(a)):
                    if a[j] != a[j + 1]:
                        return(j+1)                        

t = int(input())
for i in range(t):
    n = int(input())
    a = list(map(int, input().split()))
    print(pyranha(n, a))