#include<bits/stdc++.h>
#define ll long long
#define all(x) x.begin(), x.end()
#define lowbit(i) ((i)&(-i))
#define pii pair<int,int>
#define endl '\n'
#define mk(x,y) make_pair(x,y)
#define popcount(x) __builtin_popcount(x)
#define LF(x) fixed<<setprecision(x)
const double pi=3.14159265358979323846;
const double eps=1e-9;
const int inf=1e9;
const long long INF=4e18;
const int mod=1e9+7;
using namespace std;
const int N=1e5+10;
struct val
{
	ll a,b;
	bool vis;
};
void solve()
{
	int n,m;
	cin>>n>>m;
	int cnt=0;//更喜欢没有邻居的人数
	vector<val>x(n+1);
	for(int i=1;i<=n;i++){
		cin>>x[i].a>>x[i].b;
		if(x[i].b>x[i].a)cnt++;
		x[i].vis=false;
	}
	if(cnt==0){
		ll sum=0;
		for(int i=1;i<=n;i++){
			sum+=x[i].a;
		}
		cout<<sum<<endl;
		return;
	}
	/*
	sort(x.begin()+1,x.end(),[&](val t1,val t2){
		return t1.b>t2.b;
	});
	*/
	sort(x.begin()+1,x.end(),[&](val t1,val t2){
		return t1.b>t2.b;
	});
	vector<ll>sum1(n+1),sum2(n+1);
	for(int i=1;i<=n;i++){
		sum1[i]=sum1[i-1]+x[i].b;
		sum2[i]=sum2[i-1]+x[i].a;
	}
	ll ans=0;
	for(int i=0;i<=n;i++){
		if((n-i>=2&&i+n<=m)||(n==i&&2*n-1<=m)){
			// cout<<i<<endl;
			ll res=sum1[i];
			res+=sum2[n]-sum2[i];
			ans=max(ans,res);
		}
	}
	cout<<ans<<endl;
}

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