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

bool check(vector<int> &a,int n,int h,int mid){

    for(int i=1;i<n;i++){
        h-=min(a[i]-a[i-1],mid);
        if(h<=0)return true;
    }

    if(h<=mid)return true;
    return false;
}

int minimumJugCapacity(int N,int H,vector<int> &A){
    int start =1;
    int end = H;
    int ans = 0;
    while(start<=end){
        int mid = (start+end)/2;
        if(check(A,N,H,mid)){
            ans = mid;
            end = mid-1;
        }
        else{
            start = mid+1;
        }
    }
    return ans;
}

int main(){
    int t;
    cin>>t;
    while(t--){
        int N,H;
        cin>>N>>H;

        vector<int> A(N);
        for(int i=0;i<N;i++)cin>>A[i];
        cout<<minimumJugCapacity(N,H,A)<<endl;
    }
}