// WA 解法
// Use std::multiset<> but erase items in wrong manner
#include <algorithm>
#include <iostream>
#include <set>
#include <vector>
using namespace std;


int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int T;
    cin >> T;
    while (T--) {
        int N;
        cin >> N;
        vector<int> A(N);
        for (auto &x : A) cin >> x;
        sort(A.begin(), A.end());

        int all = A.back();
        for (int i = N - 1; i; --i) A[i] -= A[i - 1];

        multiset<int> ms;

        int last = 0;
        for (int i = 0; i < N; ++i) {
            ms.insert(A[i]);
            if (i % 2 == 0 and ms.size()) {
                int v = *prev(ms.end());
                last += v;
                ms.erase(v);
            }
        }
        cout << ((N & 1) ? last : all - last) << '\n';
    }
}