#include<bits/stdc++.h>
#define ll long long
#define int ll
const int N=1e5+10;
using namespace std;
void solve()
{
   int n,m;
   cin>>n>>m;
   vector<int>a(n+1),b(n+1),c;
   int ans=0;
   int num=0;
   for(int i=0;i<n;i++)
   {
       cin>>a[i]>>b[i];
       if(b[i]-a[i]>0)
       c.push_back(b[i]-a[i]);
       ans+=a[i];
       num+=b[i];
   }
   sort(c.begin(),c.end(),greater<int>());
   int tp=ans;
   for(int i=0;i<min(m-n,(ll)c.size());i++)
   {
       if(i==n-2)
           break;
       tp+=c[i];
   }
   if(m-n>=n-1)
       tp=max(tp,num);
   ans=max(ans,tp);
   cout<<ans<<"\n";

}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t=1;
    cin>>t;
    while(t--)
    {
        solve();
    }
}