#include <bits/stdc++.h>
using namespace std;

int n, k;
vector<long long> x;   // vi tri cac ho, da sap xep tang dan

// Kiem tra voi do dai D co the phu moi ho bang toi da k loa khong.
// Tham lam: loa dau tien dat tai vi tri ho chua duoc phu dau tien, phu den x + D; lap lai.
bool ok(long long D) {
    int cnt = 0, i = 0;
    while (i < n) {
        cnt++;
        if (cnt > k) return false;
        long long end = x[i] + D;
        while (i < n && x[i] <= end) i++;
    }
    return true;
}

// Sub 1: thu lan luot D = 0, 1, 2, ... den khi ok(D). Dung khi n <= 15 va x <= 100 (D <= 100)
void sub1() {
    for (long long D = 0;; D++)
        if (ok(D)) { cout << D << "\n"; return; }
}

// Sub 2 (day du): tim kiem nhi phan tren D trong [0, x_max - x_min]. ok(D) don dieu theo D.
// O(n log(max x)) moi truy van.
void sub2() {
    long long lo = 0, hi = x[n - 1] - x[0];
    while (lo < hi) {
        long long mid = (lo + hi) / 2;
        if (ok(mid)) hi = mid; else lo = mid + 1;
    }
    cout << lo << "\n";
}

int main() {
    freopen("CAU3.INP", "r", stdin);
    freopen("CAU3.OUT", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t--) {
        cin >> n >> k;
        x.assign(n, 0);
        for (int i = 0; i < n; i++) cin >> x[i];
        sort(x.begin(), x.end());
        if (n <= 15 && x[n - 1] <= 100) sub1();
        else sub2();
    }
    return 0;
}