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

#define fill(x,y) memset(x,y,sizeof(x))
#define fi first
#define se second
#define sz(x) ((int) (x).size())
#define all(x) (x).begin(), (x).end()
#define sqr(x) ((x) * (x))
#define sqrt(x) sqrt(abs(x))
#define mp make_pair
#define pb push_back

typedef long long ll;
typedef string s;
typedef pair<int,int> pii;
typedef pair<int,string> pis;
typedef pair<string,int> psi;
typedef pair<string,string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef vector<vector<ll> > matrix;

const ll oo = 1e6;

const double EPS = (1e-7);
int dcmp(double x, double y) {  return fabs(x-y) <= EPS ? 0 : x < y ? -1 : 1; }


int tarr[400001];
int res[100001];

void build (int index ,int l , int r){
	if(l==r){
		tarr[index]= l;
		return ;
	}
	int mid = (l+r)/2;
	build(2*index,l,mid);
	build(2*index+1,mid+1,r);
	if(res[tarr[2*index]] >= res[tarr[2*index+1]]){
		tarr[index] = tarr[2*index];
	}
	else{
		tarr[index] = tarr[2*index+1];
	}
}


void update (int index , int start , int endd , int ind){
	if(start == ind && endd == ind ){
			return;
	}
	int mid=(start+endd)/2;
	if(ind <= mid) update(2*index,start,mid,ind);
	else update(2*index+1,mid+1,endd,ind);
	if(res[tarr[2*index]] >= res[tarr[2*index+1]]){
		tarr[index] = tarr[2*index];
	}
	else{
		tarr[index] = tarr[2*index+1];
	}
}

int main(){
	ios::sync_with_stdio(0);
	int inputs;
	cin >> inputs ;
	for(int i=0 ; i<inputs ; i++){
		memset(res, 0 ,sizeof res);
		int maxy=0,maxin=0,n,q,moment,tries=0;
		cin >> n >> q ;
		build(1, 0, n-1);
		for(int j=0 ; j<q ; j++){
			int x,p ; cin >> x >> p;
			x--;
			res[x] += p;
			update(1, 0, n-1, x);
			int comp = tarr[1];
			int maxi2 = res[comp];
			if(maxi2 > maxy){
				if(comp != maxin){
					tries++;
					moment=j;
				}
				maxin=comp;
				maxy = maxi2;
			}
			else if(maxi2 == maxy){
				if(comp < maxin){
					tries++;
					moment=j;
					maxin=comp;
					maxy = maxi2;
				}
			}
		}
		if(tries==1){
			cout<<0<<endl;
		}
		else{
			cout<<(moment+1)<<endl;
		}
	}
}
/*
1
5 6
1 -2
2 -2
3 -1
2 -1
3 0
4 0*/