#include<bits/stdc++.h>
# define int long long
# define rep(i, j, k) for (int i = j; i <= k; ++i)
using namespace std;

int T, n, m, a[500005], b[500006], st[500005], tmpa[500005], tmpb[500005], ans;
bool cmp(int x, int y){return b[x] - a[x] > b[y] - a[y];}
signed main()
{
	ios::sync_with_stdio(false); cin.tie(0), cout.tie(0);
	cin >> T;
	while (T--)
	{
		cin >> n >> m;
		ans = 0;
		rep(i, 1, n) cin >> a[i] >> b[i], ans += a[i], st[i] = i;
		if (n == 1) {cout << b[1] << '\n'; continue;}
		sort(st + 1, st + n + 1, cmp);
		rep(i, 1, n) tmpa[i] = a[st[i]], tmpb[i] = b[st[i]];
		rep(i, 1, n) a[i] = tmpa[i], b[i] = tmpb[i];
		int maxx = min(n, m - n);
		if (maxx >= n - 1)
		{
			rep(i, 1, n - 2) {if (b[i] > a[i]) ans += b[i] - a[i];}
			if (b[n - 1] > a[n - 1]) ans = max(ans, ans + b[n - 1] - a[n - 1] + b[n] - a[n]);
			cout << ans << '\n';
			continue;
		}
		rep(i, 1, maxx) {if (b[i] <= a[i]) break; ans += b[i] - a[i];}
		cout << ans << '\n';
	}
	return 0;
}