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

# cook your dish here
for t in range(int(input())):
    n = int(input())
    a = list(map(int, input().split()))
    m = max(a)
    if len(set(a))==1:
        print(-1)
    else:
        for i in range(n):
            if a[i]==m:
                if (i>1 and a[i-1]!=m):  
                    print(i+1)
                    break
                if (i<n-1 and a[i+1]!=m):
                    print(i+1)
                    break