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()))
    m=max(a)
    ans=-2
    for i in range(n):
        if i==0 and a[i]==m and a[i+1]!=a[i]:
            ans=i
            break
        elif i==n-1 and a[i]==m and a[i-1]!=a[i]:
            ans=i
            break
        elif i>0 and i<n-1 and a[i]==m and (a[i+1]!=m or a[i-1]!=m):
            ans=i
            break
    print(ans+1)    
        
    