#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int tc; cin >> tc;

    test:
    while (tc--) {
        ll n; cin >> n;
        
        ll arr[n];
        for (auto &u : arr) cin >> u;
        sort(arr, arr+n);

        // ll ans = -1e18;
        // for (ll i = 1; i < n; i++) ans = max(ans, arr[i]-arr[i-1]);
        cout << arr[n-1]-arr[n-2] << "\n";
    }
}