#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
const int N = 1e6;
const int M = 2e3;
bool cmp(pii a, pii b) {
    return a.first - a.second > b.first - b.second;
}
void solve() {
    int n, m;
    cin >> n >> m;
    vector<pii> s(n + 1);
    int sum = 0;
    for (int i = 1; i <= n; i++) {
        cin >> s[i].second >> s[i].first;
        sum += s[i].second;
    }
    sort(s.begin() + 1, s.end(), cmp);
    int d = m - n;
    int cnt = 0;
    for (int i = 1; i <= d; i++) {
        if (s[i].first - s[i].second <= 0)
            break;
        sum += s[i].first - s[i].second;
        cnt++;
    }
    if (cnt== n - 1) {
        sum += s[n].first - s[n].second;
    }
    cout << sum << endl;

    return;
}
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    cin >> t;
    while (t--)
        solve();
    return 0;
}