#include <bits/stdc++.h>
using namespace std;
#define debug(x) cerr << #x << " == " << x << endl
#define el '\n'
typedef long long ll;
const int mod = 1000000007;
const int inf = 2147483647;
const int N = 500010;
int n, m, a[N], b[N], c[N], d[N];
typedef long long ll;

struct Node {
};

void solve()
{
	cin >> n >> m;
	ll ans = 0, suma = 0, sumb = 0;
	for (int i = 1; i <= n; i++) {
		cin >> a[i] >> b[i], c[i] = b[i] - a[i], d[i] = a[i] - b[i];
		ans += max(a[i], b[i]);
		suma += a[i];
		sumb += b[i];
	}
	if (n == 1) {
		cout << b[1] << endl;
		return;
	}
	if (n == 2) {
		if (m > 2)
			cout << max(a[1] + a[2], b[1] + b[2]) << endl;
		else
			cout << (a[1] + a[2]) << endl;
		return;
	}
	sort(c + 1, c + 1 + n);
	sort(d + 1, d + 1 + n);
	if (m - n >= n - 1) {
		ll nei = sumb;
		for (int i = n; i; i--) {
			if (i == n || i == n - 1)
				nei += d[i];
			else {
				if (d[i] <= 0)
					break;
				nei += d[i];
			}
		}
		cout << max(sumb, nei) << endl;
		return;
	}
	// for (int i = 1; i <= n; i++)
	//	cout << c[i] << " ";
	// cout << endl;
	for (int i = n; i >= n - (m - n) + 1; i--) {
		if (c[i] <= 0)
			break;
		suma += c[i];
	}
	cout << suma << endl;
}


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