#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define IOS {cin.tie(0);cout.tie(0);ios::sync_with_stdio(0);}
using namespace std;

typedef long long ll;
typedef pair<int,int> P;

const int N = 500050;

int a[N];

bool cmp(int a, int b) {
    return a >b;
}

int main() {
    int T; scanf("%d", &T);
    while (T--) {
        int n, m;
        ll ans =0;
        scanf("%d%d", &n, &m);
        rep (i, 1, n) {
            int x, y; scanf("%d%d", &x, &y);
            a[i] = y - x;
            ans += x;
        }
        if (n == 1) {
            cout << ans + a[1] <<'\n';
            continue;
        }
        int k = m-n;
        sort(a+1, a+n+1, cmp);
        rep (i, 1, min(k, n-2)) {
            if (a[i] > 0) ans += a[i];
        }
        if (k >= n-1) {
            ans = max(ans, ans + a[n] + a[n-1]);
        }
        cout << ans<<'\n';
    }   
 
    return 0;
}