#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
// #define max(a, b) ((a) > (b) ? (a) : (b))
// #define min(a, b) ((a) < (b) ? (a) : (b))
#define pb push_back
#define LNF 1e18
#define INF 0x7fffffff
#define int long long
#define lowbit(x) ((x) & (-x))
#define abs(x) llabs(x)
#define endl '\n'
#define Y() cout << "Yes" << endl
#define N() cout << "No" << endl
const db eps = 1e-9;
const int mod = 998244353;
const int MAXN = 2e5 + 5;

void solve()
{
    int n, k;
    cin >> n >> k;
    vector<pair<int, int>> v;
    for (int i = 1; i <= k; i++)
    {
        int a, b;
        cin >> a >> b;
        v.push_back({a, b});
    }
    sort(v.begin(), v.end(), [&](const pair<int, int> &a, const pair<int, int> &b)
         { return a.second - a.first > b.second - b.first; });
    vector<int> fa(n + 1);
    auto [l1, r1] = v[0];
    int rt = l1;
    int len = r1 - l1;
    if (len == 0)
    {
        if (n != 1)
        {
            cout << "IMPOSSIBLE" << endl;
            return;
        }
        else
        {
            cout << 0 << endl;
            return;
        }
    }
    int num = len, ma = 0;
    for (int i = 1; i < v.size(); i++)
    {
        auto [a, b] = v[i];
        if (b - a + 1 >= len)
        {
            fa[a] = rt;
            ma = max(ma, b - a + 1);
        }
        else
        {
            num += b - a + 1;
            fa[a] = rt + 1;
        }
    }
    if (ma > len+num)
    {
        cout << "IMPOSSIBLE" << endl;
    }
    else
    {
        for (auto [a, b] : v)
        {
            for (int i = a + 1; i <= b; i++)
            {
                fa[i] = i - 1;
            }
        }
        for (int i = 1; i <= n; i++)
            cout << fa[i] << " ";
        cout << endl;
    }
}
signed main()
{
    std::ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    cin >> T;
    while (T--)
        solve();
    return 0;
}