#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],sum[N];

void solve()
{
    cin >> n >> m;
    memset(sum,0,(n + 1) * sizeof(int));
    vector<array<int,2>> s;
    int ss = 0;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i] >> b[i];
        c[i] = a[i] - b[i];
        ss = ss + b[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;
    sum[1] = a[s[0][1]] + ss - b[s[0][1]];
    for(int i = 2;i < max(2ll,2 * n - m);i++)
    {
        sum[i] = sum[i - 1] - b[s[i - 1][1]] + a[s[i - 1][1]];
    }
    int mx = 0;
    for(int i = max(2ll,2 * n - m);i <= n;i++)
    {
        sum[i] = sum[i - 1] - b[s[i - 1][1]] + a[s[i - 1][1]];
        mx = max(mx,sum[i]);
    }
    ans = mx;
    if(m >= 2 * n - 1)
    {
        ans = max(ans,ss);
    }
    cout << ans << endl;
}


signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> T;
    while(T--)
    {
        solve();
    }
}