#include<bits/stdc++.h>
using namespace std;
int a[500006],b[500006],c[500006];
vector<int>du,he;
bool cmp(int a,int b){
	return c[a]>c[b];
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin>>t;
	while(t--){
		long long sum=0;
		int n,m;
		cin>>n>>m;
		
		int keyiduju=m-n;
		for(int i=1;i<=n;i++){
			cin>>a[i]>>b[i];
			c[i]=b[i]-a[i];
			sum+=a[i];
			if(a[i]<b[i])du.push_back(i);
		//	else he.push_back(i);
		}
		if(n==2&&m>n){
			int sum1=a[1]+a[2];
			int sum2=b[1]+b[2];
			cout<<(sum1>sum2?sum1:sum2)<<endl;
			continue;
		}
		if(n==1){
			cout<<(a[1]>b[1]?a[1]:b[1])<<endl;
			continue;
		}
		if(keyiduju==0)cout<<sum<<endl;
		else{
			int cnt=0;
			sort(du.begin(),du.end(),cmp);
			for(int i=0;i<keyiduju;i++){
				sum-=a[du[i]];
				sum+=b[du[i]];
			}
			cout<<sum<<endl; 
		}
		
	}
		return 0;
	
		
	}