#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }


constexpr Int INF = 1001001001001001001LL;

int N, M;
vector<Int> A, B;

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%d%d", &N, &M);
    A.resize(N);
    B.resize(N);
    for (int i = 0; i < N; ++i) {
      scanf("%lld%lld", &A[i], &B[i]);
    }
    
    Int ans = 0;
    vector<Int> ds(N);
    for (int i = 0; i < N; ++i) {
      ans += A[i];
      ds[i] = B[i] - A[i];
    }
    sort(ds.begin(), ds.end(), greater<Int>());
    vector<Int> dsSum(N + 1, 0);
    for (int i = 0; i < N; ++i) {
      dsSum[i + 1] = dsSum[i] + ds[i];
    }
    
    Int mx = -INF;
    for (int k = 0; k <= N; ++k) {
      if (N == 1 && k == 0) continue;
      if (k == N - 1) continue;
      if (k <= M - N || M >= 2 * N - 1) {
        chmax(mx, dsSum[k]);
      }
    }
    ans += mx;
    
    printf("%lld\n", ans);
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}