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

using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pll = pair<ll, ll>;

void solve() {
	int n, m;
	cin >> n >> m;
	vector<pll> a(n);

	vector<ll> lone(n);
	ll ans = 0;
	for (int i = 0; i < n; i++) {
		cin >> a[i].first >> a[i].second;
		ans += a[i].first;
		lone[i] = a[i].second - a[i].first;
	}

	if (n == 1) {
		ans = a[0].second;
		cout << ans << "\n";
		return;
	}
	if (n == 2) {
		ans = a[0].first + a[1].first;
		if (m > 2) {
			ans = max(ans, a[0].second + a[1].second);
		}
		cout << ans << "\n";
		return;
	}

	int maxlone = min(m - n, n);
	sort(rbegin(lone), rend(lone));
	for (int i = 0; i < maxlone; i++) {
		if (lone[i] < 0) break;
		if (i == n - 2) {
			ans += max(lone[i] + lone[i + 1], 0ll);
			break;
		}
		else {
			ans += lone[i];
		}
	}
	cout << ans << "\n";
}

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int t;
	cin >> t;
	while (t--) {
		solve();
	}	
}