agreesive cow

/*  TAHMID RAHMAN
    DAMIAN FOREVER
     MATH LOVER
    NEVER GIVE UP
*/
#include<bits/stdc++.h>
using namespace std;
#define pi acos(-1.0)
#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define ll long long
#define pb push_back
#define fi first
#define se second
#define in insert
#define mp make_pair
#define GCD(a,b) __gcd(a,b);
#define endl "\n"
#define FRU freopen("out.txt","w",stdout)
#define FRO freopen("in.txt","r",stdin)
#define INFLL 9223372036854775807
//Don't hesitate to ask me if you don't understand my code.......Happy coding,Tahmid...;
ll a[100001];
bool istrue(ll mid,ll n,ll c)
{
    ll cnt=0,i,pref=-INT_MAX;
    for(i=1;i<=n;i++)
    {
       if(a[i]-pref>=mid)
       {
           cnt++;
           pref=a[i];
       }
    }
    if(cnt>=c)
        return true;
    else
        return false;
}
ll bs(ll n,ll c)
{
    ll l=0,h=a[n]-a[1],mid,ans=0;
    while(l<h)
    {
        mid=(l+h)/2 ;
        if(istrue(mid,n,c))
           ans=max(ans,mid),l=mid+1;
        else
            h=mid-1;
    }
    return ans;
}

int main()
{
    fastio;
    ll t;
    cin>>t;
    while(t--)
    {
        ll n,c,i;
        cin>>n>>c;
        for(i=1;i<=n;i++)
        {
            cin>>a[i];
        }
        sort(a+1,a+n+1);
        cout<<bs(n,c)<<endl;
    }
}