text: #include<bits/stdc++.h>
  using namespace std;
  typedef long long int ll;
  
  int check(ll arr[],ll n,ll ans,ll h)
  {
      for(ll i=1;i<n;i++)
      {
          if(arr[i]-arr[i-1]>ans)
          h -= ans;
          else
          h -= (arr[i]-arr[i-1]);
      }
      h -= ans;
      if(h > 0) return 0;
      return 1;
  }
  
  int main()
  {
      ios_base::sync_with_stdio(false);
      cin.tie(NULL);
      int t;
      cin>>t;
      while(t--)
      {
          ll n,h;
          cin>>n>>h;
          ll arr[n];
          for(ll i=0;i<n;i++) cin>>arr[i];
          if(n>=h) cout<<"1"<<endl;
          else
          {
              ll low = 1 , high = h;
              while(low<high)
              {
                  ll mid = low + (high-low)/2;
                  if(check(arr,n,mid,h)) high = mid;
                  else low = mid + 1;
              }
              cout<<low<<endl;
          }
      }
      return 0;
  }