'''
Given an array A of N positive numbers.
The task is to find the position where equilibrium first occurs in the array.
Equilibrium position in an array is a position such that
the sum of elements before it is equal to the sum of elements after it.

Input:
The first line of input contains an integer T,
denoting the number of test cases.
Then T test cases follow.
First line of each test case contains an integer N
denoting the size of the array.
Then in the next line are N space separated values of the array A.

Output:
For each test case in a new line print the position at which
the elements are at equilibrium if no equilibrium point exists print -1.

Constraints:
1 <= T <= 100
1 <= N <= 106
1 <= Ai <= 108

Example:
Input:
2
1
1
5
1 3 5 2 2

Output:
1
3

Explanation:
Testcase 1: Since its the only element hence its the only equilibrium point.
Testcase 2: For second test case equilibrium point is at position 3
as elements below it (1+3) = elements after it (2+2).
'''




def findElement(arr,n):
    if n == 1:
        return 1
    elif n == 2:
        return -1
    else:
        sum_left, sum_right = arr[0], sum(arr[2:])
        for index in range(1,n - 1):
            if sum_left != sum_right:
                sum_left, sum_right = sum_left + arr[index], sum_right - arr[index + 1]
            else:
                return index
        return -1
        

T = int(input())
for i in range(T):
    n = int(input())
    a = list(map(int,input().split()))
    print(findElement(a,n))
