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: import java.util.*;
  import java.io.*;
  
  public class Practice {
  	static boolean multipleTC = true;
  	FastReader in;
  	PrintWriter out;
  
  	static int mod = (int) (1e9 + 7);
  
  	public static void main(String[] args) throws Exception {
  		new Practice().run();
  	}
  
  	void run() throws Exception {
  		in = new FastReader();
  		out = new PrintWriter(System.out);
  		int T = (multipleTC) ? ni() : 1;
  		pre();
  		for (int t = 1; t <= T; t++)
  			solve(t);
  		out.flush();
  		out.close();
  	}
  
  	void pre() throws Exception {
  	}
  
  	void solve(int TC) throws Exception {
  		int n = ni();
  		long h = nl();
  		int arr[] = readArr(n);
  		long left = 1;
  		long right = h;
  		long ans = 0;
  		// binary search template
  		while (left <= right) {
  			long mid = left + (right - left) / 2;
  			if (isValid(arr, mid, h)) {
  				right = mid - 1;
  				ans = mid;
  			} else {
  				left = mid + 1;
  			}
  		}
  		pn(ans);
  
  	}
  
  	boolean isValid(int arr[], long mid, long hitpoint) {
  		int n = arr.length;
  		long damage = 0;
  		for (int i = 0; i < n - 1; i++) {
  			damage += min(arr[i + 1] - arr[i], mid);
  		}
  		damage += mid;
  		return (damage >= hitpoint);
  	}
  
  	StringBuilder printArr(int arr[]) {
  		StringBuilder sb = new StringBuilder();
  		int n = arr.length;
  		for (int i = 0; i < n; i++) {
  			sb.append(arr[i] + " ");
  		}
  		return sb;
  	}
  
  	class pair {
  		int x, y;
  
  		pair(int x, int y) {
  			this.x = x;
  			this.y = y;
  		}
  
  		@Override
  		public String toString() {
  			return " " + x + ", " + y + "]";
  		}
  
  	}
  
  	class pairL {
  		long x, y;
  
  		pairL(long x, long y) {
  			this.x = x;
  			this.y = y;
  		}
  
  		@Override
  		public String toString() {
  			return " " + x + ", " + y + "]";
  		}
  
  	}
  
  	boolean isSorted(int arr[]) {
  		for (int i = 0; i < arr.length - 1; i++) {
  			if (arr[i] > arr[i + 1]) {
  				return false;
  			}
  		}
  		return true;
  	}
  
  	void swap(int arr[], int x, int y) {
  		int t = arr[x];
  		arr[x] = arr[y];
  		arr[y] = t;
  	}
  
  	static int bitCount(int x) {
  		return x == 0 ? 0 : (1 + bitCount(x & (x - 1)));
  	}
  
  	void sort(int arr[]) {
  		ArrayList<Integer> list = new ArrayList<>();
  		for (int i = 0; i < arr.length; i++)
  			list.add(arr[i]);
  		Collections.sort(list);
  		for (int i = 0; i < arr.length; i++)
  			arr[i] = list.get(i);
  	}
  
  	static void dbg(Object... o) {
  		System.err.println(Arrays.deepToString(o));
  	}
  
  	ArrayList<Long> primeFactorization(long n) {
  		ArrayList<Long> factorization = new ArrayList<>();
  		while (n % 2 == 0) {
  			factorization.add(2L);
  			n /= 2;
  		}
  		for (long d = 3; d * d <= n; d += 2) {
  			while (n % d == 0) {
  				factorization.add(d);
  				n /= d;
  			}
  		}
  		if (n > 1)
  			factorization.add(n);
  		return factorization;
  	}
  
  	public static boolean isPrime(long n) {
  		if (n < 2)
  			return false;
  		if (n == 2 || n == 3)
  			return true;
  		if (n % 2 == 0 || n % 3 == 0)
  			return false;
  		long sqrtN = (long) Math.sqrt(n) + 1;
  		for (long i = 6L; i <= sqrtN; i += 6) {
  			if (n % (i - 1) == 0 || n % (i + 1) == 0)
  				return false;
  		}
  		return true;
  	}
  
  	public static long gcd(long a, long b) {
  		if (a > b)
  			a = (a + b) - (b = a);
  		if (a == 0L)
  			return b;
  		return gcd(b % a, a);
  	}
  
  	public long binaryExpo(long base, long exp) {
  		long res = 1;
  		while (exp > 0) {
  			if ((exp & 1) == 1)
  				res = res * base;
  			base = base * base;
  			exp >>= 1;
  		}
  		return res;
  	}
  
  	public long pow(long base, long exp, long MOD) {
  		base %= MOD;
  		long res = 1;
  		while (exp > 0) {
  			if ((exp & 1) == 1)
  				res = res * base % MOD;
  			base = base * base % MOD;
  			exp >>= 1;
  		}
  		return res;
  	}
  
  	public static long totient(long n) {
  		long result = n;
  		for (int p = 2; p * p <= n; ++p)
  			if (n % p == 0) {
  				while (n % p == 0)
  					n /= p;
  				result -= result / p;
  			}
  		if (n > 1)
  			result -= result / n;
  		return result;
  	}
  
  	int bit(long n) {
  		return (n == 0) ? 0 : (1 + bit(n & (n - 1)));
  	}
  
  	public long max(long... arr) {
  		long max = arr[0];
  		for (long itr : arr)
  			max = Math.max(max, itr);
  		return max;
  	}
  
  	public int max(int... arr) {
  		int max = arr[0];
  		for (int itr : arr)
  			max = Math.max(max, itr);
  		return max;
  	}
  
  	public long min(long... arr) {
  		long min = arr[0];
  		for (long itr : arr)
  			min = Math.min(min, itr);
  		return min;
  	}
  
  	public int min(int... arr) {
  		int min = arr[0];
  		for (int itr : arr)
  			min = Math.min(min, itr);
  		return min;
  	}
  
  	public long sum(long... arr) {
  		long sum = 0;
  		for (long itr : arr)
  			sum += itr;
  		return sum;
  	}
  
  	public long sum(int... arr) {
  		long sum = 0;
  		for (int itr : arr)
  			sum += itr;
  		return sum;
  	}
  
  	void p(Object o) {
  		out.print(o);
  	}
  
  	void pn(Object o) {
  		out.println(o);
  	}
  
  	void pni(Object o) {
  		out.println(o);
  		out.flush();
  	}
  
  	String n() throws Exception {
  		return in.next();
  	}
  
  	String nln() throws Exception {
  		return in.nextLine();
  	}
  
  	int ni() throws Exception {
  		return Integer.parseInt(in.next());
  	}
  
  	long nl() throws Exception {
  		return Long.parseLong(in.next());
  	}
  
  	int[] readArr(int n) throws Exception {
  		int arr[] = new int[n];
  		for (int i = 0; i < n; i++) {
  			arr[i] = ni();
  		}
  		return arr;
  	}
  
  	double nd() throws Exception {
  		return Double.parseDouble(in.next());
  	}
  
  	class FastReader {
  		BufferedReader br;
  		StringTokenizer st;
  
  		public FastReader() {
  			br = new BufferedReader(new InputStreamReader(System.in));
  		}
  
  		public FastReader(String s) throws Exception {
  			br = new BufferedReader(new FileReader(s));
  		}
  
  		String next() throws Exception {
  			while (st == null || !st.hasMoreElements()) {
  				try {
  					st = new StringTokenizer(br.readLine());
  				} catch (IOException e) {
  					throw new Exception(e.toString());
  				}
  			}
  			return st.nextToken();
  		}
  
  		String nextLine() throws Exception {
  			String str = "";
  			try {
  				str = br.readLine();
  			} catch (IOException e) {
  				throw new Exception(e.toString());
  			}
  			return str;
  		}
  	}
  }