#include <bits/stdc++.h>
using namespace std;
#define int long long
#define x first
#define y second
#define endl '\n'
typedef pair<int,int> PII;
const int N = 5e5 + 10,INF = 1e18;
int T,n,m;
int a[N],b[N],c[N];

void solve()
{
    cin >> n >> m;
    vector<array<int,2>> s;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i] >> b[i];
        c[i] = b[i] - a[i];
        s.push_back({c[i],i});
    }
    if(n == 1)
    {
        cout << b[1] << endl;
        return ;
    }
    sort(s.begin(),s.end());
    reverse(s.begin(),s.end());
    int ans = 0;
    int x = 0;
    for(int i = 0;i < min(m - n,n);i++)
    {
        if(s[i][0] > 0) 
        {
            ans = ans + b[s[i][1]];
            x++;
        }
        else break;
    }
    if(x == n - 1)
    {
        if(a[s[x][1]] - b[s[x][1]] > b[s[x - 1][1]] - a[s[x - 1][1]]) 
            ans = ans + a[s[x][1]] + a[s[x - 1][1]] - b[s[x - 1][1]];
        else
            ans = ans + b[s[x][1]];
    }
    else{
        for(int i = x;i < n;i++) ans = ans + a[s[i][1]];    
    }
    cout << ans << endl;
}


signed main()
{
//	freopen("data.in","r",stdin);
// 	freopen("me.out","w",stdout);
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> T;
    while(T--)
    {
        solve();
    }
}