description: Monocarp is playing yet another computer game. In this game, his character has to kill a dragon. The battle with the dragon lasts 100^{500} seconds, during which Monocarp attacks the dragon with a poisoned dagger. The i-th attack is performed at the beginning of the a_i-th second from the battle start. The dagger itself does not deal damage, but it applies a poison effect on the dragon, which deals 1 damage during each of the next k seconds (starting with the same second when the dragon was stabbed by the dagger). However, if the dragon has already been poisoned, then the dagger updates the poison effect (i.e. cancels the current poison effect and applies a new one).
  
  For example, suppose k = 4, and Monocarp stabs the dragon during the seconds 2, 4 and 10. Then the poison effect is applied at the start of the 2-nd second and deals 1 damage during the 2-nd and 3-rd seconds; then, at the beginning of the 4-th second, the poison effect is reapplied, so it deals exactly 1 damage during the seconds 4, 5, 6 and 7; then, during the 10-th second, the poison effect is applied again, and it deals 1 damage during the seconds 10, 11, 12 and 13. In total, the dragon receives 10 damage.
  
  Monocarp knows that the dragon has h hit points, and if he deals at least h damage to the dragon during the battle — he slays the dragon. Monocarp has not decided on the strength of the poison he will use during the battle, so he wants to find the minimum possible value of k (the number of seconds the poison effect lasts) that is enough to deal at least h damage to the dragon.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 1000) — the number of test cases.
  
  The first line of the test case contains two integers n and h (1 ≤ n ≤ 100; 1 ≤ h ≤ 10^{18}) — the number of Monocarp's attacks and the amount of damage that needs to be dealt.
  
  The second line contains n integers a_1, a_2, ..., a_n (1 ≤ a_i ≤ 10^9; a_i < a_{i + 1}), where a_i is the second when the i-th attack is performed.
  
  Output
  
  For each test case, print a single integer — the minimum value of the parameter k, such that Monocarp will cause at least h damage to the dragon.
  
  Example
  
  Input
  
  
  4
  2 5
  1 5
  3 10
  2 4 10
  5 3
  1 2 4 5 7
  4 1000
  3 25 64 1337
  
  
  Output
  
  
  3
  4
  1
  470
  
  Note
  
  In the first example, for k=3, damage is dealt in seconds [1, 2, 3, 5, 6, 7].
  
  In the second example, for k=4, damage is dealt in seconds [2, 3, 4, 5, 6, 7, 10, 11, 12, 13].
  
  In the third example, for k=1, damage is dealt in seconds [1, 2, 4, 5, 7].
solution: #Mamma don't raises quitter.................................................
  #manan is improving, keep hustling manan bhai ;)
  from collections import deque as de
  import math
  import sys
  from math import sqrt as sq
  from math import floor as fl
  from math import ceil as ce
  from sys import stdin, stdout
  import time
  
  sys.setrecursionlimit(10**7)
  from collections import Counter as cnt
  from functools import  reduce
  
  from itertools import groupby as gb
  #from fractions import Fraction as fr
  from bisect import bisect_left as bl, bisect_right as br
  from typing import Coroutine
  
  def factors(n):    
      return set(reduce(list.__add__, 
                  ([i, n//i] for i in range(1, int(n**0.5) + 1) if n % i == 0)))
      
  class My_stack():
      def __init__(self):
          self.data = []
      def my_push(self, x):
          return (self.data.append(x))
      def my_pop(self):
          return (self.data.pop())
      def __iter__(self):
          return iter(self.data)
      def my_peak(self):
          return (self.data[-1])
      def my_contains(self, x):
          return (self.data.count(x))
      def my_show_all(self):
          return (self.data)
      def isEmpty(self):
        return len(self.data)==0
      def len(self):
          return len(self.data)
      
  
  arrStack = My_stack() 
  
  class graph():
      def __init__(self):
          self.graphdict = {}
      def add_edge(self, node, neighbor):
          if node not in self.graphdict:
              self.graphdict[node]=[neighbor]
          else:
              self.graphdict[node].append(neighbor)
      def show_edge(self):
          for node in self.graphdict:
              for neighbors in self.graphdict:
                  print(node, neighbors)
      def show_graph(self):
          return self.graphdict
  
      
  
  
      
              
  
  #decimal to binary   
  def decimalToBinary(n): 
      return bin(n).replace("0b", "")
  #binary to decimal
  def binarytodecimal(n):
      return int(n,2)
  
  def isPrime(n) : 
  	if (n <= 1) : 
  		return False
  	if (n <= 3) : 
  		return True
  	if (n % 2 == 0 or n % 3 == 0) : 
  		return False
  	i = 5
  	while(i * i <= n) : 
  		if (n % i == 0 or n % (i + 2) == 0) : 
  			return False
  		i = i + 6
  	return True
  
  def get_prime_factors(number):
      prime_factors = []
      while number % 2 == 0:
          prime_factors.append(2)
          number = number / 2
      for i in range(3, int(math.sqrt(number)) + 1, 2):
          while number % i == 0:
              prime_factors.append(int(i))
              number = number / i
  
      if number > 2:
          prime_factors.append(int(number))
      return prime_factors
  
  def get_frequency(list):
      dic={}
      for ele in list:
          if ele in dic:
              dic[ele] += 1
          else:
              dic[ele] = 1
      return dic
  
  def Log2(x): 
      return (math.log10(x) / 
              math.log10(2)); 
  
   
  # Function to get product of digits
  def getProduct(n):
      product = 1
      while (n != 0):
          product = product * (n % 10)
          n = n // 10
      return product
  #fucntion to find regular bracket sequence
  def regularBracketsequence(str,arrStack):
      for i in range(len(str)):
          if str[i] =='(':
              arrStack.my_push(str[i])
          else:
              if arrStack.isEmpty():
                  return False
              else:
                  arrStack.my_pop()
      if arrStack.isEmpty():
          return True
      else:
          return False
  
  #function to find LCM of two numbers
  def lcm(x,y):
     lcm = (x*y)//math.gcd(x,y)
     return lcm
  
  def isPowerOfTwo(n): 
      return (math.ceil(Log2(n)) == math.floor(Log2(n))); 
  #to check whether the given sorted sequnce is forming an AP or not....
  def checkisap(list):
      d=list[1]-list[0]
      for i in range(2,len(list)):
          temp=list[i]-list[i-1]
          if temp !=d:
              return False
      return True
  
  #seive of erathanos
  def primes_method5(n):
      out ={}
      sieve = [True] * (n+1)
      for p in range(2, n+1):
          if (sieve[p]):
              out[p]=1
              for i in range(p, n+1, p):
                  sieve[i] = False
      return out
  #fucntion to get unique number to a cell in a matrix
  def id(i, j, col): #one based indexing and columnwise numeration
      ans= (i-1)*col
      ans+=j
      return ans
  
  #function to get the sum of digits
  def getSum(n): 
        
      strr = str(n)
      list_of_number = list(map(int, strr.strip()))
      return sum(list_of_number)
  def checkperfectsquare(n):
      if (ce(sq(n)) == fl(sq(n))):
          return True
      else:
          return False
  #this used for selecting r objects from n ojects
  def combinatrics(n,r):
      num=n
      deno=n-r
      pr=1
      for i in range(num,deno,-1):
          pr*=i
      an=1
      for i in range(1,r+1):
          an*=i
      ans=pr//an
      return ans
  #ceil  function gives wrong answer after 10^17 so i have to create my own :)
  # because i don't want to doubt on my solution of 900-1000 problem set.
  def ceildiv(x,y): 
      return (x+y-1)//y 
    
  def di():return map(int, input().split())
  def ii():return int(input())
  def li():return list(map(int, input().split()))
  def si():return list(map(str, input()))
  def indict():
      dic = {}
      for index, value in enumerate(input().split()):
          dic[int(value)] = int(index)
      return dic
  def frqdict(): 
      # by default it is for integer input. :)
      dic={}
      for index, value in enumerate(input()):
          if value not in dic:
              dic[value] =1
          else:
              dic[value] +=1
      return dic
  
  #sys.stdin = open('input.txt', 'r')
  #sys.stdout = open('output.txt', 'w')
  #practice like your never won
  #perform like you never lost
  t=ii()
  while t:
      t-=1
      n,h=di()
      a=li()
      if n==1:
          print(h)
      elif n==2:
          diff=a[1]-a[0]
          if 2*diff==h:
              print(diff)
          elif 2*diff> h:
              print(ceildiv(h,2))
          else:
              print(h-diff)
      else:
          temp=[]
          for i in range(1, n):
              temp.append(a[i]-a[i-1])
          temp.sort()
          #print(temp)
          s=0
          for i in range(len(temp)):
              s+=temp[i]
              tempsum=s+(temp[i]*(n-i-1))
              if tempsum >=h:
                  #print(temp[i])
                  break
          if tempsum >=h:
              s-=temp[i]
              ans=ceildiv(h-s,n-i)
              print(ans)
          else:
              print(h-s)
          
  
      