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 piranha(A):
    M = max(A)
    res = -1
    if len(set(A)) == 1:
        return -1
    n = len(A)    
    for i in range(n):
        if A[i] == M and ((i < n-1 and A[i] > A[i+1]) or (i > 0 and A[i] > A[i-1])):
            res = i+1
            break
    return res

if __name__ == "__main__":
    t = int(input())
    for _ in range(t):
        n = int(input())
        A = list(map(int,input().split()))
        res = piranha(A)
        print(res)