def main():
    T = int(input())
    for i in range(T):
        N = int(input())
        A = sorted(map(int, input().split()))
        a = s = 0
        for i in range(N-1, -1, -1):
            v = A[i] - (A[i-1] if i != 0 else 0)
            a = max(a, s-a)
            s += v
            if ((N-1)-i) % 2 == 0:
                a += v
        print(a)


if __name__ == '__main__':
    main()