/* GREEN UNIVERSITY OF BANGLADESH
    Md DinIslam, Batch-221 (CSE)
*/
#include <bits/stdc++.h>
using namespace std;

// Debug..
#ifdef LOCAL
#include "debug.h"
#else
#define dg(x...)
#endif

#define ll long long
#define all(x) x.begin(), x.end()
#define pb push_back
#define sz(x) int(x.size())
#define arr array

void Din() {
    int n;
    cin >> n;

    vector<int> v(n);
    for (auto &x : v) {
        cin >> x;
    }

    sort(all(v), greater());

    ll ans = v[0] - v[1];

    // cout << max(ans, 0ll) << '\n';
    cout << ans << "\n";
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t = 1;
    cin >> t;
    for (int i = 1; i <= t; ++i) {
        // cout << "Case " << i << ": ";
        Din();
    }
    return 0;
}