#include <bits/stdc++.h>
using namespace std;
typedef std::pair<int, int> ipair;
#define int long long
#define pb push_back
#define ff first
#define ss second
#define fr(i, j, k) for (int i = j; i < k; i++)
#define cnt_ones(x) __builtin_popcount(x)
#define all(x) x.begin(), x.end()
#define mp make_pair
#define mod 1000000007
#define IOS                                                                    \
  std::ios::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);

int findSmallestRange(vector<vector<int>>b,int k) {
  int i, minval, maxval, minrange, minel, maxel, flag, minind;
    int ptr[k+1];
  // initializing to 0 index;
  for (i = 0; i <= k; i++)
    ptr[i] = 0;

  minrange = INT_MAX;

  while (1) {
    // for mainting the index of list containing the minimum element
    minind = -1;
    minval = INT_MAX;
    maxval = INT_MIN;
    flag = 0;

    // iterating over all the list
    for (i = 0; i < k; i++) {
      // if every element of list[i] is traversed then break the loop
      if (ptr[i] == b[i].size()) {
        flag = 1;
        break;
      }
      // find minimum value among all the list elements pointing by the ptr[]
      // array
      if (ptr[i] < b[i].size() && b[i][ptr[i]] < minval) {
        minind = i; // update the index of the list
        minval = b[i][ptr[i]];
      }
      // find maximum value among all the list elements pointing by the ptr[]
      // array
      if (ptr[i] < b[i].size() && b[i][ptr[i]] > maxval) {
        maxval = b[i][ptr[i]];
      }
    }

    // if any list exhaust we will not get any better answer ,so break the while
    // loop
    if (flag)
      break;

    ptr[minind]++;

    // updating the minrange
    if ((maxval - minval) < minrange) {
      minel = minval;
      maxel = maxval;
      minrange = maxel - minel;
    }
  }

  return minrange;
}
void init() {
  int T;
  cin >> T;
  while (T--) {
    int N,M;
    cin>>N>>M;
    vector<vector<int>>b(M);
    vector<int>a(N);
    for(int i=0;i<N;i++)    cin>>a[i];
    for(int i=0;i<N;i++)
        b[i%M].pb(a[i]);
    for(int i=0;i<M;i++){
        sort(b[i].begin(),b[i].end());
    }
    int res=findSmallestRange(b,M);
    cout<<res<<endl;
  }
}
int32_t main() {
  IOS;
  init();
  return 0;
}