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())
    arr=list(map(int,input().split()))
    ans=-2
    a=max(arr)
    for i in range(n):
        if i==0 and arr[i]==a and arr[i+1]!=arr[i]:
            ans=0
            break
        elif i==n-1 and arr[i]==a and arr[i-1]!=arr[i]:
            ans=n-1
            break
        elif i> 0 and i<n-1 and arr[i]==a and (arr[i-1]!=arr[i] or arr[i+1]!=arr[i]):
            ans=i
            break
    print(ans+1)



