Agg_cow

#include <bits/stdc++.h>
using namespace std;
typedef int l;
typedef long long int ll;
#define loop(a, b) for(int i = a; i < b; i++)

void run(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output7.txt", "w", stdout);
#else
#endif
}

bool check(ll ara[], l n, l m, ll mid){
    m--;
    l current = 0;
    l j = 1;
    while(j < n){
        if(abs(ara[current] - ara[j]) >= mid){
            current = j;
            m--;
        }
        if(m <= 0) return true;
        j++;
    }
    return false;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    //run();
    l t;cin>>t;
    while(t--){
        l n, m;cin>>n>>m;
        ll ara[n];loop(0, n) cin>>ara[i];
        sort(ara, ara+n);
        ll left = 2, right = abs(ara[n-1] - ara[0]);
        while(left <= right){
            l mid = left + ((right - left) >> 1);
            if(check(ara, n, m, mid)) left = mid + 1;
            else right = mid - 1;
        }
        cout << right << endl;
    }
    return 0;
}