# region template

from platform import node
from typing import Generic, Iterable, Iterator, TypeVar, Union, List
from bisect import bisect_left, bisect_right, insort
from re import A
import typing
import math
import sys
import copy
import itertools
import collections
import bisect
import heapq
import decimal


def ni(): return int(sys.stdin.readline())
def ns(): return map(int, sys.stdin.readline().split())
def ns1(): return map(lambda x: int(x)-1, sys.stdin.readline().split())
def na(): return list(map(int, sys.stdin.readline().split()))
def na1(): return list(map(lambda x: int(x)-1, sys.stdin.readline().split()))
def nall_i(): return list(map(int, sys.stdin.read().split()))
def nall_s(): return list(map(str, sys.stdin.read().split()))
def flush(): return sys.stdout.flush()
def nib(): return int(sys.stdin.buffer.readline())
def nsb(): return map(int, sys.stdin.buffer.readline().split())
def ns1b(): return map(lambda x: int(x)-1, sys.stdin.buffer.readline().split())
def nab(): return list(map(int, sys.stdin.buffer.readline().split()))
def na1b(): return list(map(lambda x: int(x)-1, sys.stdin.buffer.readline().split()))
def nallb(): return list(map(int, sys.stdin.buffer.read().split()))
# limregion


# sys.setrecursionlimit(10**7+1)
inf = 10**23
# mod = 10**9+7
mod = 998244353


def main():
    # https://open.spotify.com/track/6ldZaRUFcKh908SJXwdbZj?si=383824f68a8a47c0
    def solve():
        N = ni()
        A = na()
        A.sort()

        B = [A[0] if i == 0 else A[i]-A[i-1] for i in range(N)]

        hq = []
        res = 0
        for i, bi in enumerate(B):
            heapq.heappush(hq, -bi)
            if i % 2 == 0:
                res += -heapq.heappop(hq)

        print(res if N % 2 else A[-1]-res)

    T = ni()
    for _ in range(T):
        solve()


if __name__ == '__main__':
    main()