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

t=int(input())
for _ in range(t):
    n=int(input())
    l=list(map(int,input().split()))
    mx=max(l)
    #print(mx)
    c=l.count(mx)
    
    mxind=[]
    for i in range(n):
        if l[i]==mx:
            mxind.append(i)
            
    #print(mxind)
    flag=0
    ind=-99
    for i in range(len(mxind)-1):
        if mxind[i+1]-mxind[i]>1:
            ind=mxind[i+1]
            flag=1
            break
    if mxind[-1]!=n-1:
        ind=mxind[-1]
    elif mxind[0]!=0:
        ind=mxind[0]

    
    if c==n:
        print(-1)
    else:
        print(ind+1)