#include<bits/stdc++.h>
using namespace std;
#define ll long long int 
int main()
{
    ll tc;
    cin>>tc;
    while(tc--)
    {
     ll n;
        cin>>n;
        vector<ll>v(n);
        for(int i=0;i<n;i++)
            cin>>v[i];
        sort(v.rbegin(),v.rend());
        cout<<v[0]-v[1]<<endl;
    
    }
}