#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> a(2 * n);
    for (int i = 0; i < 2 * n; ++i) {
      cin >> a[i];
    }
    sort(a.begin(), a.end());
    ll ans = 0;
    for (int i = 0; i < 2 * n; ++i) {
      ans += (i < n ? -1 : 1) * a[i];
    }
    cout << ans << '\n';
  }
}