description: Yelisey has an array a of n integers.
  
  If a has length strictly greater than 1, then Yelisei can apply an operation called minimum extraction to it: 
  
    1. First, Yelisei finds the minimal number m in the array. If there are several identical minima, Yelisey can choose any of them. 
    2. Then the selected minimal element is removed from the array. After that, m is subtracted from each remaining element. 
  
  
  
  Thus, after each operation, the length of the array is reduced by 1.
  
  For example, if a = [1, 6, -4, -2, -4], then the minimum element in it is a_3 = -4, which means that after this operation the array will be equal to a=[1 {- (-4)}, 6 {- (-4)}, -2 {- (-4)}, -4 {- (-4)}] = [5, 10, 2, 0].
  
  Since Yelisey likes big numbers, he wants the numbers in the array a to be as big as possible.
  
  Formally speaking, he wants to make the minimum of the numbers in array a to be maximal possible (i.e. he want to maximize a minimum). To do this, Yelisey can apply the minimum extraction operation to the array as many times as he wants (possibly, zero). Note that the operation cannot be applied to an array of length 1.
  
  Help him find what maximal value can the minimal element of the array have after applying several (possibly, zero) minimum extraction operations to the array.
  
  Input
  
  The first line contains an integer t (1 ≤ t ≤ 10^4) — the number of test cases.
  
  The next 2t lines contain descriptions of the test cases.
  
  In the description of each test case, the first line contains an integer n (1 ≤ n ≤ 2 ⋅ 10^5) — the original length of the array a. The second line of the description lists n space-separated integers a_i (-10^9 ≤ a_i ≤ 10^9) — elements of the array a.
  
  It is guaranteed that the sum of n over all test cases does not exceed 2 ⋅ 10^5.
  
  Output
  
  Print t lines, each of them containing the answer to the corresponding test case. The answer to the test case is a single integer — the maximal possible minimum in a, which can be obtained by several applications of the described operation to it.
  
  Example
  
  Input
  
  
  8
  1
  10
  2
  0 0
  3
  -1 2 0
  4
  2 10 1 7
  2
  2 3
  5
  3 2 -4 -2 0
  2
  -1 1
  1
  -2
  
  
  Output
  
  
  10
  0
  2
  5
  2
  2
  2
  -2
  
  Note
  
  In the first example test case, the original length of the array n = 1. Therefore minimum extraction cannot be applied to it. Thus, the array remains unchanged and the answer is a_1 = 10.
  
  In the second set of input data, the array will always consist only of zeros.
  
  In the third set, the array will be changing as follows: [\color{blue}{-1}, 2, 0] → [3, \color{blue}{1}] → [\color{blue}{2}]. The minimum elements are highlighted with \color{blue}{blue}. The maximal one is 2.
  
  In the fourth set, the array will be modified as [2, 10, \color{blue}{1}, 7] → [\color{blue}{1}, 9, 6] → [8, \color{blue}{5}] → [\color{blue}{3}]. Similarly, the maximum of the minimum elements is 5.
solution: 
  import java.io.*;
  import java.lang.reflect.Array;
  import java.util.*;
  
  public class Main {
  
      static class Pair {
          int x,y;
  
          public Pair(int x,int y) {
              this.x=x;
              this.y=y;
          }
      }
  
      static int mod=1000000007;
  
      public static void main(String[] args) throws IOException
      {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          OutputWriter out = new OutputWriter(outputStream);
          TaskC solver = new TaskC();
          solver.solve(1, in, out);
          out.close();
      }
  
      static class TaskC
      {
          public static void solve(int testNumber, InputReader in, OutputWriter out)
          {
              int t=in.readInt();
              while(t-->0)
              {
                  int n=in.readInt();
                  int arr[]=in.nextIntArray(n);
                  if(n==1)
                  {
                      out.printLine(arr[0]);
                      continue;
                  }
                  CP.sort(arr);
                  long prev=0,ele=0;
                  int min=Integer.MIN_VALUE;
                  for(int i=0;i<n;i++)
                  {
                      min=Math.max(min,(int)(arr[i]-prev));
                      prev=prev+arr[i]-prev;
                  }
                  out.printLine(min);
              }
          }
      }
  
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private InputReader.SpaceCharFilter filter;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          public int read() {
              if (numChars == -1) {
                  throw new InputMismatchException();
              }
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
                  if (numChars <= 0) {
                      return -1;
                  }
              }
              return buf[curChar++];
          }
  
          public int readInt() {
              int c = read();
              while (isSpaceChar(c)) {
                  c = read();
              }
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              int res = 0;
              do {
                  if (c < '0' || c > '9') {
                      throw new InputMismatchException();
                  }
                  res *= 10;
                  res += c - '0';
                  c = read();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
  
          public int[] nextIntArray(int arraySize) {
              int[] array = new int[arraySize];
  
              for (int i = 0; i < arraySize; i++) {
                  array[i] = readInt();
              }
  
              return array;
          }
  
          public String readString() {
              int c = read();
              while (isSpaceChar(c)) {
                  c = read();
              }
              StringBuilder res = new StringBuilder();
              do {
                  if (Character.isValidCodePoint(c)) {
                      res.appendCodePoint(c);
                  }
                  c = read();
              } while (!isSpaceChar(c));
              return res.toString();
          }
  
          public boolean isNewLine(int c) {
              return c == '\n';
          }
  
          public String nextLine() {
              int c = read();
  
              StringBuilder result = new StringBuilder();
  
              do {
                  result.appendCodePoint(c);
  
                  c = read();
              } while (!isNewLine(c));
  
              return result.toString();
          }
  
          public long nextLong() {
              int c = read();
  
              while (isSpaceChar(c)) {
                  c = read();
              }
  
              int sign = 1;
  
              if (c == '-') {
                  sign = -1;
  
                  c = read();
              }
  
              long result = 0;
  
              do {
                  if (c < '0' || c > '9') {
                      throw new InputMismatchException();
                  }
  
                  result *= 10;
                  result += c & 15;
  
                  c = read();
              } while (!isSpaceChar(c));
  
              return result * sign;
          }
  
          public long[] nextLongArray(int arraySize) {
              long array[] = new long[arraySize];
  
              for (int i = 0; i < arraySize; i++) {
                  array[i] = nextLong();
              }
  
              return array;
          }
  
          public double nextDouble() {
              double ret = 0, div = 1;
              byte c = (byte) read();
  
              while (c <= ' ') {
                  c = (byte) read();
              }
  
              boolean neg = (c == '-');
  
              if (neg) {
                  c = (byte) read();
              }
  
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = (byte) read()) >= '0' && c <= '9');
  
              if (c == '.') {
                  while ((c = (byte) read()) >= '0' && c <= '9') {
                      ret += (c - '0') / (div *= 10);
                  }
              }
  
              if (neg) {
                  return -ret;
              }
  
              return ret;
          }
  
          public boolean isSpaceChar(int c) {
              if (filter != null) {
                  return filter.isSpaceChar(c);
              }
              return isWhitespace(c);
          }
  
          public static boolean isWhitespace(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          public interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
  
          }
      }
  
      static class CP {
  
          static boolean isPrime(long n) {
              if (n <= 1)
                  return false;
              if (n == 2 || n == 3)
                  return true;
              if (n % 2 == 0 || n % 3 == 0)
                  return false;
              for (int i = 5; (long) i * i <= n; i += 6) {
                  if (n % i == 0 || n % (i + 2) == 0)
                      return false;
              }
              return true;
          }
  
          static String addChar(String s, int n, String ch) {
              String res =s+String.join("", Collections.nCopies(n, ch));
              return res;
          }
  
          static int ifnotPrime(int[] prime, int x) {
  
              return (prime[x / 64] & (1 << ((x >> 1) & 31)));
          }
  
          static void makeComposite(int[] prime, int x) {
  
              prime[x / 64] |= (1 << ((x >> 1) & 31));
          }
  
          static ArrayList<Integer> bitWiseSieve(int n) {
              ArrayList<Integer> al = new ArrayList<>();
              int prime[] = new int[n / 64 + 1];
  
  
              for (int i = 3; i * i <= n; i += 2) {
  
                  if (ifnotPrime(prime, i) == 0)
                      for (int j = i * i, k = i << 1;
                           j < n; j += k)
                          makeComposite(prime, j);
              }
  
              al.add(2);
  
              for (int i = 3; i <= n; i += 2)
                  if (ifnotPrime(prime, i) == 0)
                      al.add(i);
  
              return al;
          }
  
          public static long[] sort(long arr[]){
              List<Long> list = new ArrayList<>();
              for(long n : arr){list.add(n);}
              Collections.sort(list);
              for(int i=0;i<arr.length;i++){
                  arr[i] = list.get(i);
              }
              return arr;
          }
  
  
          static List<Integer> sieve(long size) {
  
              ArrayList<Integer> pr = new ArrayList<Integer>();
              boolean prime[] = new boolean[(int) size];
              for (int i = 2; i < prime.length; i++) prime[i] = true;
              for (int i = 2; i * i < prime.length; i++) {
                  if (prime[i]) {
                      for (int j = i * i; j < prime.length; j += i) {
                          prime[j] = false;
                      }
                  }
              }
              for (int i = 2; i < prime.length; i++) if (prime[i]) pr.add(i);
              return pr;
          }
  
          static void segmented_sieve(int l, int r, ArrayList<Integer> primes) {
              if (l == 1) ++l;
              int max = r - l + 1;
              int arr[] = new int[max];
              for (int p : primes) {
                  if (p * p <= r) {
                      int i = (l / p) * p;
                      if (i < l) i += p;
                      for (; i <= r; i += p) {
                          if (i != p) {
                              arr[i - l] = 1;
                          }
                      }
                  }
              }
              for (int i = 0; i < max; ++i) {
                  if (arr[i] == 0) {
                      System.out.println(l + i);
                  }
              }
          }
  
          static boolean isfPrime(long n, int iteration) {
  
              if (n == 0 || n == 1)
                  return false;
  
              if (n == 2)
                  return true;
  
              if (n % 2 == 0)
                  return false;
  
              Random rand = new Random();
              for (int i = 0; i < iteration; i++) {
                  long r = Math.abs(rand.nextLong());
                  long a = r % (n - 1) + 1;
                  if (modPow(a, n - 1, n) != 1)
                      return false;
              }
              return true;
          }
  
          static long modPow(long a, long b, long c) {
              long res = 1;
              for (int i = 0; i < b; i++) {
                  res *= a;
                  res %= c;
              }
              return res % c;
          }
  
          private static long binPower(long a, long l, long mod) {
  
              long res = 0;
  
              while (l > 0) {
                  if ((l & 1) == 1) {
                      res = mulmod(res, a, mod);
                      ;
                      l >>= 1;
                  }
                  a = mulmod(a, a, mod);
              }
              return res;
          }
  
          private static long mulmod(long a, long b, long c) {
  
              long x = 0, y = a % c;
              while (b > 0) {
                  if (b % 2 == 1) {
                      x = (x + y) % c;
                  }
                  y = (y * 2L) % c;
                  b /= 2;
              }
              return x % c;
  
          }
  
          static long binary_Expo(long a, long b) {
              long res = 1;
              while (b != 0) {
                  if ((b & 1) == 1) {
                      res *= a;
                      --b;
                  }
                  a *= a;
                  b /= 2;
              }
              return res;
          }
  
          static long Modular_Expo(long a, long b) {
              long res = 1;
              while (b != 0) {
                  if ((b & 1) == 1) {
                      res = (res * a) % 1000000007;
                      --b;
                  }
                  a = (a * a) % 1000000007;
                  b /= 2;
              }
              return res;
          }
  
          static int i_gcd(int a, int b) {
              while (true) {
                  if (b == 0)
                      return a;
                  int c = a;
                  a = b;
                  b = c % b;
              }
          }
  
          static long gcd(long a, long b) {
              if (b == 0)
                  return a;
              return gcd(b, a % b);
          }
  
          static long ceil_div(long a, long b) {
              return (a + b - 1) / b;
          }
  
          static int getIthBitFromInt(int bits, int i) {
              return (bits >> (i - 1)) & 1;
          }
  
          private static TreeMap<Long, Long> primeFactorize(long n) {
              TreeMap<Long, Long> pf = new TreeMap<>(Collections.reverseOrder());
              long cnt = 0;
              long total = 1;
              for (long i = 2; (long) i * i <= n; ++i) {
                  if (n % i == 0) {
                      cnt = 0;
                      while (n % i == 0) {
                          ++cnt;
                          n /= i;
                      }
                      pf.put(cnt, i);
                      //total*=(cnt+1);
                  }
              }
              if (n > 1) {
                  pf.put(1L, n);
                  //total*=2;
              }
              return pf;
          }
  
          static long upper_Bound(long a[], long x) {
              long l = -1, r = a.length;
              while (l + 1 < r) {
                  long m = (l + r) >>> 1;
                  if (a[(int) m] <= x)
                      l = m;
                  else
                      r = m;
              }
              return l + 1;
          }
  
          static int upper_Bound(List<Integer> a, int x) {
              int l = -1, r = a.size();
              while (l + 1 < r) {
                  int m = (l + r) >>> 1;
                  if (a.get(m) <= x)
                      l = m;
                  else
                      r = m;
              }
              return l + 1;
          }
  
          static int lower_Bound(int a[],int x) {
              int l = -1, r = a.length;
              while (l + 1 < r) {
                  int m = (l + r) >>> 1;
                  if (a[(int) m] >= x)
                      r = m;
                  else
                      l = m;
              }
              return r;
          }
  
          static long bsh(int  a[],int t) {
              int ans = -1;
              int i = 0, j = a.length - 1;
              while (i <= j) {
                  int mid = i + (j - i) / 2;
                  if (a[mid] == t) {
                      ans = mid;
                      break;
                  } else if (a[mid] > t) {
                      ans = mid;
                      j = mid - 1;
                  } else {
                      i = mid + 1;
                  }
              }
              return ans;
          }
  
          static int bsl(int a[],int t) {
              int ans = -1;
              int i = 0, j = a.length - 1;
              while (i <= j) {
                  int mid = i + (j - i) / 2;
                  if (a[mid] == t) {
                      ans = mid;
                      break;
                  } else if (a[mid] > t) {
                      j = mid - 1;
                  } else {
                      ans=mid;
                      i = mid + 1;
                  }
              }
              return ans;
          }
  
          static int lower_Bound(List<Integer> a, int x)  //closest to the right
          {
              int l = -1, r = a.size();
              while (l + 1 < r) {
                  int m = (l + r) >>> 1;
                  if (a.get(m) >= x)
                      r = m;
                  else
                      l = m;
              }
              return r;
          }
  
          static boolean isSquarefactor(int x, int factor, int target) {
              int s = (int) Math.round(Math.sqrt(x));
              return factor * s * s == target;
          }
  
          static boolean isSquare(int x) {
              int s = (int) Math.round(Math.sqrt(x));
              return x * x == s;
          }
  
          static void sort(int a[]) // heap sort
          {
              PriorityQueue<Integer> q = new PriorityQueue<>();
              for (int i = 0; i < a.length; i++)
                  q.add(a[i]);
              for (int i = 0; i < a.length; i++)
                  a[i] = q.poll();
          }
  
          static void shuffle(int[] in) {
              for (int i = 0; i < in.length; i++) {
                  int idx = (int) (Math.random() * in.length);
                  fast_swap(in, idx, i);
              }
          }
  
          static int[] computeLps(String pat) {
              int len = 0, i = 1, m = pat.length();
              int lps[] = new int[m];
              lps[0] = 0;
              while (i < m) {
                  if (pat.charAt(i) == pat.charAt(len)) {
                      ++len;
                      lps[i] = len;
                      ++i;
                  } else {
                      if (len != 0) {
                          len = lps[len - 1];
                      } else {
                          lps[i] = len;
                          ++i;
                      }
                  }
              }
              return lps;
          }
  
          static void kmp(String s, String pat) {
              int n = s.length(), m = pat.length();
              int lps[] = computeLps(pat);
              int i = 0, j = 0;
              while (i < n) {
                  if (s.charAt(i) == pat.charAt(j)) {
                      i++;
                      j++;
  
                  } else {
                      if (j != 0) {
                          j = lps[j - 1];
                      } else {
                          i++;
                      }
                  }
              }
          }
  
          static void reverse_ruffle_sort(int a[]) {
              shuffle(a);
              Arrays.sort(a);
              for (int l = 0, r = a.length - 1; l < r; ++l, --r)
                  fast_swap(a, l, r);
  
          }
  
          static void ruffle_sort(int a[]) {
              shuffle(a);
              Arrays.sort(a);
          }
  
          static int getMax(int arr[], int n) {
              int mx = arr[0];
              for (int i = 1; i < n; i++)
                  if (arr[i] > mx)
                      mx = arr[i];
              return mx;
          }
  
          static ArrayList<Long> primeFactors(long n) {
              ArrayList<Long> al = new ArrayList<>();
              al.add(1L);
              while (n % 2 == 0) {
                  if(!al.contains(2L))
                  {
                      al.add(2L);
                  }
                  n /= 2L;
              }
  
              for (int i = 3; (long) i * i <= n; i += 2) {
                  while ((n % i == 0)) {
                      if(!al.contains((long)i))
                      {
                          al.add((long) i);
                      }
                      n /= i;
                  }
              }
  
              if (n > 2) {
                  if(!al.contains(n))
                  {
                      al.add(n);
                  }
              }
              return al;
          }
  
          static int[] z_function(String s) {
              int n = s.length(), z[] = new int[n];
  
              for (int i = 1, l = 0, r = 0; i < n; ++i) {
                  if (i <= r)
                      z[i] = Math.min(z[i - l], r - i + 1);
  
                  while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i]))
                      ++z[i];
  
                  if (i + z[i] - 1 > r) {
                      l = i;
                      r = i + z[i] - 1;
                  }
              }
              return z;
          }
  
          static void swap(int a[], int idx1, int idx2) {
              a[idx1] += a[idx2];
              a[idx2] = a[idx1] - a[idx2];
              a[idx1] -= a[idx2];
          }
  
          static void fast_swap(int[] a, int idx1, int idx2) {
              if (a[idx1] == a[idx2])
                  return;
  
              a[idx1] ^= a[idx2];
              a[idx2] ^= a[idx1];
              a[idx1] ^= a[idx2];
          }
  
          public static void fast_sort(long[] array) {
              ArrayList<Long> copy = new ArrayList<>();
              for (long i : array)
                  copy.add(i);
              Collections.sort(copy);
              for (int i = 0; i < array.length; i++)
                  array[i] = copy.get(i);
          }
  
          static int divCount(int n) {
              boolean hash[] = new boolean[n + 1];
              Arrays.fill(hash, true);
              for (int p = 2; p * p < n; p++)
                  if (hash[p] == true)
                      for (int i = p * 2; i < n; i += p)
                          hash[i] = false;
  
              int total = 1;
              for (int p = 2; p <= n; p++) {
                  if (hash[p]) {
                      int count = 0;
                      if (n % p == 0) {
                          while (n % p == 0) {
                              n = n / p;
                              count++;
                          }
                          total = total * (count + 1);
                      }
                  }
              }
              return total;
          }
  
          static long binomialCoeff(int n,int k)
          {
              long res = 1;
  
              // Since C(n, k) = C(n, n-k)
              if (k > n - k)
                  k = n - k;
  
              // Calculate value of
              // [n * (n-1) *---* (n-k+1)] / [k * (k-1) *----* 1]
              for (int i = 0; i < k; ++i) {
                  res = (res%mod*(n - i)%mod)%mod;
                  res /= (i + 1);
              }
              return res%mod;
          }
  
          static long c(long fact[],int n,int k)
          {
              if(k>n) return 0;
              long res=fact[n];
              res= (int) ((res * Modular_Expo(fact[k], mod - 2))%mod);
              res= (int) ((res * Modular_Expo(fact[n - k], mod - 2))%mod);
              return res%mod;
          }
  
          public static ArrayList<Long> getFactors(long x) {
  
              ArrayList<Long> facts=new ArrayList<>();
              for(long i=2;i*i<=x;++i)
              {
                  if(x%i==0)
                  {
                      facts.add(i);
                      if(i!=x/i)
                      {
                          facts.add(x/i);
                      }
                  }
              }
              return facts;
          }
      }
  
      static void py() {
          System.out.println("YES");
      }
  
      static void pn() {
          System.out.println("NO");
      }
  
      static class OutputWriter {
          private final PrintWriter writer;
  
          public OutputWriter(OutputStream outputStream) {
              writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
          }
  
          public OutputWriter(Writer writer) {
              this.writer = new PrintWriter(writer);
          }
  
          public void print(int[] array) {
              for (int i = 0; i < array.length; i++) {
                  if (i != 0) {
                      writer.print(' ');
                  }
                  writer.print(array[i]);
              }
          }
  
          public void printLine(int[] array) {
              print(array);
              writer.println();
          }
  
          public void close() {
              writer.close();
          }
  
          public void printLine(long i) {
              writer.println(i);
          }
  
          public void printLine(int i) {
              writer.println(i);
          }
          public void printLine(char c)
          {
              writer.println(c);
          }
  
          public void print(Object... objects) {
              for (int i = 0; i < objects.length; i++) {
                  if (i != 0) {
                      writer.print(' ');
                  }
                  writer.print(objects[i]);
              }
          }
  
          public void printLine(Object... objects) {
              print(objects);
              writer.println();
          }
      }
  }
  
  
  
  
  