#include <bits/stdc++.h>
using namespace std;
using ll = long long;
void solve(){
	int n, m;
	std::cin >> n >> m;
	std::vector<ll> a(n), b(n);
	std::vector<int> idx(n);
	for(int i = 0; i < n; idx[i] = i, i++) std::cin >> a[i] >> b[i];
	std::sort(idx.begin(), idx.end(), [&](int x, int y) {return a[x] - b[x] < a[y] - b[y];});
	std::vector<ll> suma(n + 1), sumb(n + 1); suma[0] = 0; sumb[0] = 0;
	for(int i = 1; i <= n; i++) {
		int j = idx[i - 1];
		suma[i] = suma[i - 1] + a[j];
		sumb[i] = sumb[i - 1] + b[j];
	}
//	for(int i = 1; i <= n; i++) {
////		int j = idx[i];
//		std::cout << suma[i] << " " << sumb[i] << '\n';
//	}
	ll ans = 0;
	for(int i = 0; i <= m - n; i++) {
		if(i > n) break;
		ll sum = sumb[i] + suma[n] - suma[i];
		if(i == n - 1) {
			sum = sumb[n];	
		}
		ans = std::max(sum, ans);
	}
	std::cout << ans << '\n';
	
}
int main()
{
	int t = 1;
	std::cin >> t;
	while(t--) solve();
}