#include <cstdio>
#include <algorithm>
#define FR(a,b) for ( int i = a ; i < b ; i++ )

using namespace std;
int t,k,n;
long long vetor[100000];
long long menor;

int main(){
	scanf("%d",&t);
	FR(0,t)
	{
		menor = 1000000000;
		scanf("%d %d",&n,&k);
		for ( int j = 0 ; j < n ; j++ )
			scanf("%d",&vetor[j]);
		sort(vetor, vetor + n);
		for ( int j = 0 ; k-1+j != n ; j++ )
			if ( vetor[k-1+j]-vetor[j] < menor )
				menor = vetor[k-1+j]-vetor[j];
		printf("%lld\n",menor);
	}
	return 0;
}