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

const int maxN = 100010;
long long dist[maxN];
long long n,c;

bool yes (long long d) {
	long long cow = c;
	long long prev_loc = dist[1];
	--cow;
	vector<int> loc;
	loc.push_back(dist[1]);
	for (int i = 2; i <= n; ++i) {
		if (dist[i] - prev_loc >= d) {
			loc.push_back(dist[i]);
			--cow;
			prev_loc = dist[i];
		}
		if (cow == 0) {
			return true;
		}
	}
	return false;
}

int main () {
	 ios::sync_with_stdio(false);
	 cin.tie(nullptr);
	 cout.tie(nullptr);
	 int T;
	 cin >> T;
	 for (int test_case = 1; test_case <= T; ++test_case) {
		cin >> n >> c;
		for (int i = 1; i <= n; ++i) cin >> dist[i];
		sort (dist + 1,dist + n + 1);
		long long res = 0;
		long long l = 1,r = dist[n];
		while (l <= r) {
			long long mid = l + (r - l) / 2;
			if (yes(mid)) {
				l = mid + 1;
				res = mid;
			} else {
				r = mid - 1;
			}
		}
		cout << res << '\n';
		//~ cout << dist[1] << ' ';
		//~ --c;
		//~ long long prev_loc = dist[1];
		//~ for (int i = 1; i <= n; ++i) {
			//~ if (dist[i] - prev_loc >= res) {
				//~ cout << dist[i] << ' ';
				//~ --c;
			//~ }
			//~ if (c == 0) break;
		//~ }
	 }
	 //~ cerr << "Time elapsed :" << clock() * 1000.0 / CLOCKS_PER_SEC << " ms" << '\n';
}

Problem Link : https://www.spoj.com/problems/AGGRCOW/