#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <set>
#include <queue>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int mod = 1000000007;

vector<int> g[300005];

int main() {
    int t;
    cin >> t;
    while (t--) {
        int n, u, v;
        cin >> n;
        for (int i = 1; i <= n; i++) g[i].clear();
        vector<int> a(n * 2 + 1), c(n * 2 + 1);
        for (int i = 1; i < n * 2; i++) cin >> a[i], c[a[i]] = 1;
        a[1] = a[n * 2 - 1] = 1; c[1] = 1;
        set<pii> s;
        for (int i = 2; i < n * 2; i++) if (a[i] && a[i - 1]) {
            pii x = {min(a[i], a[i - 1]), max(a[i], a[i - 1])};
            if (s.find(x) == s.end()) s.insert(x);
            else s.erase(x);
        }
        for (pii i : s) g[i.first].push_back(i.second), g[i.second].push_back(i.first);
        queue<int> q;
        int e = 0, f = 0, y = 0, w = 0;
        for (int i = 1; i < n * 2; i++) {
            if (!a[i]) y = 1;
            if (!a[i] && !w) w = i;
            if (a[i] && y == 1) y = 2;
            if (!y) e = a[i];
            if (y == 2 && !f) f = a[i];
        }
        vector<int> b = {e}, z;
        q.push(e);
        while (b.back() != f) {
            int x = q.front();
            q.pop();
            for (int i : g[x]) {
                if (b.size() == 1 || i != b[(int)b.size() - 2]) {
                    q.push(i);
                    b.push_back(i);
                    break;
                }
            }
        }
        set<int> t;
        for (int i = 1; i <= n; i++) if (!c[i]) t.insert(i);
        //for (int i : t) cout << i << ' '; cout << '\n';
        for (int i = 0; i < b.size(); i++) {
            z.push_back(b[i]);
            if (t.empty()) continue;
            while (i == (int)b.size() - 1 || *t.begin() < b[i + 1]) {
                vector<int> x = {b[i], *t.begin()};
                z.push_back(*t.begin());
                t.erase(t.begin());
                while (x.size() > 1) {
                    int u = (!t.empty() ? *t.begin() : n + 1), v = x[(int)x.size() - 2];
                    if (u < v) {
                        x.push_back(u);
                        z.push_back(u);
                        t.erase(t.begin());
                    } else {
                        x.pop_back();
                        z.push_back(x.back());
                    }
                }
                if (t.empty()) break;
            }
        }
        //for (int i : b) cout << i << ' '; cout << ',';
        //for (int i : z) cout << i << ' '; cout << '\n';
        for (int i = 1; i + 1 < z.size(); i++) a[i + w - 1] = z[i];
        for (int i = 1; i < n * 2; i++) cout << a[i] << " \n"[i == n * 2 - 1];
    }
}