#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
using namespace std;
using namespace __gnu_pbds;
const int N = 5e5 + 5;
int t;
int n , k;
pair < int , int > arr[N];
typedef tree < pair < int , int > , null_type , less < pair < int , int > > , rb_tree_tag , tree_order_statistics_node_update > ordered_set;
ordered_set shit;
int ans;
int main(	){
	scanf("%d" , &t);
	while(t--){
		scanf("%d %d" , &n , &k);
		for(int i = 1 ; i <= n ; ++i){
			scanf("%d %d" , &arr[i].second , &arr[i].first);
		}
		sort(arr + 1 , arr + 1 + n);
		shit.clear();
		ans = 0;
		for(int i = n ; i >= 1 ; --i){
			int j = i;
			shit.insert(make_pair(arr[i].second , i));
			while(j > 1 && arr[j - 1].first == arr[j].first){
				--j;
				shit.insert(make_pair(arr[j].second , j));
			}
			if(shit.size() >= k){
				ans = max(ans , arr[i].first - shit.find_by_order(k - 1) -> first);
			}
			i = j;
		}
		printf("%d\n" , ans);
	}
}