#include <cstdio>
#include <algorithm>

#define KONJ 42 - 42
#define MAXN 100042

using namespace std;

int T, N, K;
int niz[MAXN];

bool greedy( int value ){

    int last = N - 1, tmp = K - 1;
    for ( int i = N - 1; i >= 0; --i ){
        if ( niz[last] - niz[i] >= value ){ --tmp; last = i; }
    }

    if ( tmp <= 0 ){ return true; }
    return false;

}

int binary_search( int begin, int end ){

    int mid;
    while ( begin + 1 != end ){
        mid = ( begin + end ) / 2;
        if ( greedy( mid ) ){ begin = mid; } else { end = mid; }
    }
    if ( greedy( begin ) ){ return begin; }
    return mid;

}

void solve(){

    scanf( "%d%d", &N, &K );
    for ( int i = 0; i < N; ++i ){
        scanf( "%d", &niz[i] );
    }

    sort( niz, niz + N );
    printf( "%d\n", binary_search( 0, niz[N - 1] ) );

}

int main( void ){

    scanf( "%d", &T );
    for ( int t = 0; t < T; ++t ){
        solve();
    }

    return KONJ;

}