best time to buy stock

//Enter code here
import java.util.*;
import java.io.*;
class Main{
    static class FastReader
  {
    BufferedReader br;
    StringTokenizer st;
    public FastReader()
    {
      br = new BufferedReader(new InputStreamReader(System.in));
    }
    String next()
    {
      while (st == null || !st.hasMoreElements()){
        try { st = new StringTokenizer(br.readLine()); }
        catch (IOException e) { e.printStackTrace(); }
      }
      return st.nextToken();
    }
    int nextInt() { return Integer.parseInt(next()); }
    long nextLong() { return Long.parseLong(next()); }
    double nextDouble(){ return Double.parseDouble(next()); }
    String nextLine(){
      String str = "";
      try { str = br.readLine(); }
      catch (IOException e) { e.printStackTrace(); }
      return str;
    }
  }
  public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
       int tc = sc.nextInt();
       for(int ii=0;ii<tc;ii++){
      int n = sc.nextInt();
    //   int k = sc.nextInt();
      int[] a = new int[n];
      
      for(int i=0;i<n;i++){
          a[i] = sc.nextInt();
      }
     System.out.println(callW(a,n));

    }
  }
  
   public static int callW(int[] a,int n){
       int pro=0;
    //   int ind = -1;
   
       int smallest = Integer.MAX_VALUE;
       for(int i=0;i<n;i++){
           if(a[i]<smallest){
               smallest = a[i];
           
           }
           int cu = a[i]- smallest;
           if(cu>pro){
               pro = cu;
           }
           
           
       }
    //   for(int i=ind;i<n;i++){
    //       if(a[i] - smallest > pro){
    //           pro = a[i]-smallest;
    //       }
    //   }
       return pro;
       
   }
}