#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i=(a);i>=(b);--i)
#define pb push_back
#define eb emplace_back
#define SZ(x) ((int)(x).size())
#define D(...) fprintf(stderr,__VA_ARGS__)
using namespace std;
using LL=long long;
const int N=200005;
int T,n,m,idx;
vector<int>e[N];
int ans[N];
int main(){
#ifdef xay5421
	freopen("a.in","r",stdin);
#endif
	cin>>T;
	while(T--){
		cin>>n>>m;
		rep(i,0,n-1)e[i].clear();
		rep(i,0,n-1){
			e[i].pb((i+1)%n);
			e[(i+1)%n].eb(i);
		}
		rep(i,0,m-1){
			int u,v;
			cin>>u>>v;
			e[u].pb(v),e[v].pb(u);
		}
		rep(i,0,n-1)ans[i]=1e9;
		ans[0]=0;
		queue<int>que;
		que.push(0);
		while(!que.empty()){
			int u=que.front();
			que.pop();
			for(auto&x:e[u])if(ans[u]+1<ans[x])ans[x]=ans[u]+1;
		}
		
		rep(i,1,n)printf("%c",ans[i]&1?'B':'R');
		puts("");
	}
	return 0;
}