#include <bits/stdc++.h>

using namespace std;
#define ll long long
#define pii pair<int, int>
#define ld long double
#define all(a) (a).begin(), (a).end()

void solve() {
    int n, m;
    cin >> n >> m;
    vector<pair<int, int>> A(n);
    for (int i = 0; i < n; ++i)
        cin >> A[i].first >> A[i].second;
    if (n == 1) {
        cout << A[0].second << '\n';
        return;
    }
    int mx_solo = m == 2 * n - 1 ? n : min(n, m - n);
    sort(A.begin(), A.end(), [](const pair<int, int>& first, const pair<int, int>& second) {
        return first.second - first.first > second.second - second.first;
    });
    int cnt_pos = 0;
    while (cnt_pos < n && A[cnt_pos].second > A[cnt_pos].first)
        ++cnt_pos;
    int cur_cnt = min(mx_solo, min(n - 2, cnt_pos));
    long long ans = 0;
    for (int i = 0; i < cur_cnt; ++i)
        ans += A[i].second;
    for (int i = cur_cnt; i < n; ++i)
        ans += A[i].first;
    if (mx_solo == n) {
        long long other_ans = 0;
        for (int i = 0; i < n; ++i)
            other_ans += A[i].second;
        ans = max(ans, other_ans);
    }
    cout << ans << '\n';
}

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

    int t;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}