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

#define int long long

bool cmp(pair<int, int> a, pair<int, int> b) {
    return a.first + a.second > b.first + b.second;
}

void solve()
{
    int n;
    cin >> n;
    vector<pair<int, int>> p(n);
    for (int i = 0; i < n; i++)
    {
        cin >> p[i].first >> p[i].second;
    }

    sort(p.begin(), p.end(), cmp);
    int as = 0, bs = 0;
    for (int i = 0; i < n; i += 2)
    {
        as += p[i].first;
        if (i+1 < n) bs += p[i+1].second;
    }
    cout << as - bs << '\n';
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);

    int t;
    cin >> t;
    while (t--)
    {
        solve();
    }

    return 0;
}