#include <bits/stdc++.h>
using namespace std;

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

    int T; cin >> T;
    while (T--) {
        int N; cin >> N;
        vector<long long> A(N);
        for (int i = 0; i < N; i++) cin >> A[i];

        sort(A.rbegin(), A.rend());  // Sort descending

        long long result = 0;
        for (int i = 0; i < N; i++) {
            if (i % 2 == 0) 
                result += A[i];  // Roy's turn (0-based even)
            else
                result -= A[i];  // Hridoy's turn (0-based odd)
        }
        cout << result << "\n";
    }

    return 0;
}