#include <bits/stdc++.h>
 #define ll long long
 #define ull unsigned long long
 #define pi 3.141592654
 #define NUM 1e18
 #define Mod  1'000'000'007
 #define fixed(n) fixed<<setprecision(n)
 #define cin(v) for(auto &i:v) cin >> i ;
 #define cout(v) for(auto &i:v) cout << i  <<" ";
 #define vowel(x) (x=='e'||x=='a'||x=='i'||x=='o'||x=='u')
 #define small(x) (x>=97&&x<=122)
 #define capital(x) (x>=65&&x<=90)
 #define Tolower(s) transform(s.begin(),s.end(),s.begin(),::tolower);
 #define Toupper(s) transform(s.begin(),s.end(),s.begin(),::toupper);
 #define sz(x) (int)(x.size())
 #define all(v) ((v).begin()), ((v).end())
 #define allr(v) ((v).rbegin()), ((v).rend())
 #define updmax(a,b) a=max(a,b)
 #define updmin(a,b) a=min(a,b)
 #define ceil(a,b) ((a/b)+(a%b?1:0))
 /* asc -> 1 2 3 ,des -> 3 2 1 */

 /***********************************************************************************/
 using namespace std;
 void Rofyda_Elghadban(){
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
   #endif
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
 }

 bool BS(ll n,ll k,vector<ll>&v,ll s){
  ll temp=v[0]+s;
  int counter=1;
  for(int i=1;i<n;i++){
    if(v[i]>=temp){
      temp=v[i]+s;
      counter++;
    }else{
      continue;
    }
  }
  if(counter<=k){
    return true;
  }else{
    return false;
  }
 }

 void solve(){
  ll n,k;
  cin>>n>>k;
  vector<ll>v(n);
  cin(v);
  ll l=0,r=1e9,ans=0;
  while(l<=r){
    ll mid=l+(r-l)/2;
    if(BS(n,k,v,mid)){
      ans=mid;
      r=mid-1;
    }else{
      l=mid+1;
    }
  }
  cout<<ans<<"\n";
 }

 int main(){
  Rofyda_Elghadban();
  int t;
  cin>>t;
  while(t--){
    solve();
  }
  // solve();
  return 0;
 }