#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef long double ld;
string h;
int n,R;

 int poi[100009];
 set<pair<int,int>> sr;
   int main()
{
    int t;
    cin>>t;
    while(t--){
            sr.clear();
            int n,q;
            cin>>n>>q;
            int lw,ans;
            lw=ans=0;
            lw=1;
             memset(poi,0,sizeof poi);

                for(int i=0;i<n;i++)sr.insert({0,-1*(i+1)});
             for(int i=0;i<q;i++)
            {
                 int x,y;
                scanf("%d%d",&x,&y);
                sr.erase({poi[x],-x});
                poi[x]+=y;
                sr.insert({poi[x],-x});
                auto it=sr.end();
                it--;
                if(lw!=-1*(it->second))
                {
                    lw=-1*(it->second);
                    ans=i+1;

                }
            }
            cout<<ans<<endl;
    }





    return 0;
}