#include <bits/stdc++.h>

/*

#include <vector>

#include <iostream>

#include <queue>

#include <cmath>

#include <map>

#include <cstring>

#include <algorithm>

#include <cstdio>

*/

using namespace std;

#define For(i,j,n) for(int i=j;i<=n;i++)

#define Riep(n) for(int i=1;i<=n;i++)

#define Riop(n) for(int i=0;i<n;i++)

#define Rjep(n) for(int j=1;j<=n;j++)

#define Rjop(n) for(int j=0;j<n;j++)

#define mst(ss,b) memset(ss,b,sizeof(ss));

typedef  long long LL;

template<class T> void read(T&num) {

    char CH; bool F=false;

    for(CH=getchar();CH<''||CH>'';F= CH=='-',CH=getchar());

    for(num=;CH>=''&&CH<='';num=num*+CH-'',CH=getchar());

    F && (num=-num);

}

int stk[], tp;

template<class T> inline void print(T p) {

    if(!p) { puts(""); return; }

    while(p) stk[++ tp] = p%, p/=;

    while(tp) putchar(stk[tp--] + '');

    putchar('\n');

}

const LL mod=1e9+;

const double PI=acos(-1.0);

const LL inf=1e18;

const int N=1e5+;

const int maxn=;

const double eps=1e-;

int n;

int a[N];

int main()

{

        int t;

        read(t);

        while(t--)

        {

            read(n);

            For(i,,n)read(a[i]);

            int mmax=a[],ans=-;

            For(i,,n)

            {

                ans=max(ans,mmax-a[i]);

                if(a[i]>mmax)mmax=a[i];

            }

            cout<<ans<<"\n";

        }

        return ;

}