#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
inline ll read() {
	   ll 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 << 1) + (x << 3) + (ch ^ '0');
			ch = getchar();
	   }
	   return x * f;
}
const int N = 5e5 + 10;
int t, n, m;
struct person{
	ll x, y; bool flag;
}a[N], b[N];
bool cmp(person c, person d) {
	return c.y - c.x > d.y - d.x;
}
//!!!!!!!!!!注意，前面已经统计了答案了 
int main() {
	t = read();
	while (t--) { 
		n = read(), m = read(); ll ans = 0, arr = 0;
		for (int i = 1; i <= n; i++) {
			a[i].x = read(), a[i].y = read();
			if (a[i].x >= a[i].y) {
				ans += a[i].x, arr++, a[i].flag = 0;
			}
			else a[i].flag = 1;
		} 
		if (arr >= 2) {
			int tot = 0;
			for (int i = 1; i <= n; i++) {
				if (a[i].flag) b[++tot] = a[i];
			}
			sort(b + 1, b + tot + 1, cmp);
			//int las = m - arr; int k = n - arr;
			int sum = m - n;//las - k
			for (int i = 1; i <= tot ; i++) {
				if (sum > 0) {
					sum--; ans += b[i].y;
				} else {
					ans += b[i].x;
				}
			}
			printf("%lld\n",ans);
		} else if (arr == 0) {//!!!!!!!!!!!!!!!!!!!!!!!test
			int tot = 0;
			for (int i = 1; i <= n; i++) {
				if (a[i].flag) b[++tot] = a[i];
			}
			sort(b + 1, b + tot + 1, cmp);
			//int las = m - arr; int k = n - arr;
			int sum = m - n;//las - k
			if (sum == n - 1) sum++;
			for (int i = 1; i <= tot ; i++) {
				if (sum > 0) {
					sum--; ans += b[i].y;
				} else {
					ans += b[i].x;
				}
			}
			printf("%lld\n",ans);
		} else {
			while(1);
			ans = 0;
			int tot = 0;
			for (int i = 1; i <= n; i++) {
				b[++tot] = a[i];
			}
			sort(b + 1, b + tot + 1, cmp);
			//int las = m - arr; int k = n - arr;
			int sum = m - n;//las - k
			if (sum == n - 1) sum++;
			for (int i = 1; i <= tot ; i++) {
				if (sum > 0) {
					sum--; ans += b[i].y;
				} else {
					ans += b[i].x;
				}
			} ll anss = ans;
			ans = b[tot].x + b[tot-1].x; tot -= 2;
			sum = m - n;
			for (int i = 1; i <= tot ; i++) {
				if (sum > 0) {
					sum--; ans += b[i].y;
				} else {
					ans += b[i].x;
				}
			} anss = max(anss, ans);
			printf("%lld\n",anss);
		}
		
	}
	return 0;
}