def solve():
    N = int(input())
    A = list(map(int,input().split()))
    A.sort()
    if N % 2:
        ans = A[0]
        for i in range(1,N,2):
            ans += A[i+1] - A[i]
        print(max(ans, A[N//2]))
    else:
        ans = 0
        for i in range(0,N,2):
            ans += A[i+1] - A[i]
        print(ans)

T = int(input())
for _ in range(T):
    solve()