#include <bits/stdc++.h>
using namespace std;
#define all(x, y) x.begin() + y, x.end()
#define mkp make_pair
#define pii pair<int, int>
#define pil pair<int, long long>
#define pli pair<long long, int>
#define pll pair<long long, long long>
#define ll long long
#define ull unsigned long long
#define pb push_back
#define rep(name, base, limit) for(int name = base; name <= limit; ++name)
#define per(name, base, limit) for(int name = base; name >= limit; --name)
#define lowbit(x) ((x) & -(x))
#define ls(p) ((p) << 1)
#define rs(p) ((p) << 1 | 1)
const int INF = 0x3f3f3f3f;
const long long LNF = 0x3f3f3f3f3f3f3f3f;

inline long long read()
{
    long long x=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
    while (ch>='0'&&ch<='9'){x=x*10+ch-48;ch=getchar();}
    return x*f;
}
void solve()
{
    int n = read(), m = read(), k = m - n;
    vector<ll> a(n + 1), b(n + 1);
    rep(i, 1, n) a[i] = read(), b[i] = read();
    if (n == 1) return (void)(cout << b[1]);
    priority_queue<ll> pq;
    ll ans = 0;
    if (m >= n * 2 - 1) rep(i, 1, n) ans += b[i];
    rep(i, 1, n) pq.push(b[i] - a[i]);
    ll now = 0;
    rep(i, 1, n) now += a[i];
    ans = max(ans, now);
    rep(i, 1, min(n - 2, k))
    {
        now += pq.top();
        pq.pop();
        ans = max(ans, now);
    }
    cout << ans;
}

int main()
{
    int t = read();
    while (t--)
    {
        solve();
        if (t) putchar('\n');
    }
    return 0;
}