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

int main()
{
    int t;
    cin>>t;
    while(t--)
    {
       
        int n, k;
        cin >> n >> k;
        vector<array<int, 3>> seg(k);
        vector<int> ans(n + 1);
        map<int, int> c;
        for (int i = 0; i < k; i ++ ){
            cin >> seg[i][1] >> seg[i][2];
            seg[i][0] = seg[i][1] - seg[i][2];
            c[seg[i][0]]++;
        }
        sort(seg.begin(),seg.end());
        if(seg[0][0] == 0 || k == n){
            cout << "IMPOSSIBLE" << endl;
            continue;
        }
        int r = seg[0][1];
        //cout << c[seg[0][0]] << "!";
        if(c[seg[0][0]] == 1){
            for (int i = 0; i < k; i ++ ){
                for (int j = seg[i][1]; j <= seg[i][2]; j ++ ){
                    if(j == r){
                        ans[j] = 0;
                        continue;
                    }
                    if(j == seg[i][1]){
                        ans[j] = r;
                        continue;
                    }        
                    ans[j] = j - 1;
                }
            }            
        }
        else{
            int ok = 0;
            for(auto [x, y] : c){
                if(-x <= -seg[0][0] - 2){
                    ok = 1;
                    break;
                }
            }
            if(ok == 0){
                cout << "IMPOSSIBLE" << endl;
                continue;                
            }
            for (int i = 0; i < k - 1; i ++ ){
                for (int j = seg[i][1]; j <= seg[i][2]; j ++ ){
                    if(j == r){
                        ans[j] = 0;
                        continue;
                    }
                    if(j == seg[i][1]){
                        ans[j] = r;
                        continue;
                    }        
                    ans[j] = j - 1;
                }
            }      
            ans[seg[k - 1][1]] = seg[0][1] + 1;
            for (int i = seg[k - 1][1] + 1; i <= seg[k - 1][2]; i ++ ){
                ans[i] = i - 1;
            }
        }

        for (int i = 1; i <= n; i ++ ) cout << ans[i] << " ";
        cout << endl;
    }
}