#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
#include <algorithm>
#define pb push_back
#define mp make_pair
#define x first
#define y second

using namespace std;

typedef long double ld;
typedef long long ll;
using pii = pair<int, int>;
using vpii = vector<pii>;
using vi = vector<int>;

ll find_ans(const vpii& v, const int m) {
	const int n = v.size();
	if (n == 1) return v.front().y;
	ll s = 0;
	vi y(n);
	for (int i = 0; i < n; ++i) {
		y[i] = v[i].y - v[i].x;
		s += v[i].x;
	}
	int max_sep = m - n;
	if (m >= 2 * n - 1) max_sep = n;
	ll ans = s;
	sort(y.rbegin(), y.rend());
	for (int sep = 1; sep <= max_sep; ++sep) {
		s += y[sep - 1];
		if (sep != n - 1)
			ans = max(ans, s);
	}
	return ans;
}

void solve_test() {
	int n, m;
	cin >> n >> m;
	vpii v(n);
	for (int i = 0; i < n; ++i)
		cin >> v[i].x >> v[i].y;
	cout << find_ans(v, m) << '\n';
}

void solve_tests() {
	int t = 1;
	cin >> t;
	for (int i = 0; i < t; ++i)
		solve_test();
}

int main() {
#ifdef HOME
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	ios_base::sync_with_stdio(0); cin.tie(0);
	solve_tests();
	return 0;
}