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

void solve(){
	int n,m;cin>>n>>m;
	vector<int> c(n+1);
	vector<vector<int> > g(n+1);
	for(int i=0;i<n;i++){
		c[i]=-1;
		g[i].push_back((i+1)%n);
		g[i].push_back((i-1+n)%n);
	}
	for(int i=1;i<=m;i++){
		int u,v;cin>>u>>v;
		g[u].push_back(v);g[v].push_back(u);
	}
	queue<int> q;
	q.push(0);
	c[0]=0;
	while(q.size()){
		int x=q.front();q.pop();
		for(auto it:g[x])if(c[it]==-1){
			c[it]=1-c[x];
			q.push(it);		
		}
	}
	for(int i=0;i<n;i++){
		if(c[i]==0){
			cout<<"R";
		}
		else cout<<"B";
	}
	cout<<"\n";
}
signed main(){
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
	int T;cin>>T;
	while(T--)
	solve(); 
}