#include <bits/stdc++.h>
#define rep(i,j,k) for(int i=(j);i<=(k);i++)
#define per(i,j,k) for(int i=(j);i>=(k);i--)
#define uint unsigned int
#define ll long long
#define ull unsigned long long
#define db double
#define ldb long double
#define pii pair<int,int>
#define pll pair<ll,ll>
#define mkp make_pair
#define eb emplace_back
#define SZ(S) (int)S.size()
//#define mod 998244353
//#define mod 1000000007
#define inf 0x3f3f3f3f
#define linf 0x3f3f3f3f3f3f3f3f
using namespace std;

template <class T>
void chkmax(T &x,T y){
	if(x < y) x = y;
}

template <class T>
void chkmin(T &x,T y){
	if(x > y) x = y;
}

inline int popcnt(int x){
	return __builtin_popcount(x);
}

inline int ctz(int x){
	return __builtin_ctz(x);
}


/*ll power(ll p,int k = mod - 2){
	ll ans = 1;
	while(k){
		if(k % 2 == 1) ans = ans * p % mod;
		p = p * p % mod;
		k /= 2;	
	}
	return ans;
}*/
int T,n,m;
set <int> G[200005];

void add(int u,int v){
	G[u].insert(v);G[v].insert(u);
}

void del(int u,int v){
	assert(G[u].count(v));
	G[u].erase(v);G[v].erase(u);
}

int a[200005],adj[200005][2],ans[200005];
vector <int> ord,Q;
void solve(){
	scanf("%d%d",&n,&m);
	rep(u,1,n){
		G[u].clear();
		adj[u][0] = adj[u][1] = 0;
	}
	rep(i,1,n - 1) add(i,i + 1);
	add(1,n);
	rep(i,1,m){
		int u,v;
		scanf("%d%d",&u,&v);
		u++;v++;
		add(u,v);
	}
	ord.clear();Q.clear();
	rep(u,1,n) if(SZ(G[u]) <= 2) Q.eb(u);
	while(!Q.empty()){
		int u = Q.back();
		Q.pop_back();
		ord.eb(u);
		for(int v:G[u]){
			if(!adj[u][0]) adj[u][0] = v;
			else if(!adj[u][1]) adj[u][1] = v;
			else assert(0);
		}
		if(adj[u][0]) del(u,adj[u][0]);
		if(adj[u][1]) del(u,adj[u][1]);
		if(adj[u][0] && adj[u][1]) add(adj[u][0],adj[u][1]);
	}
	while(!ord.empty()){
		int u = ord.back();
		ord.pop_back();
		ans[u] = 0;
		if(!ans[adj[u][0]] || !ans[adj[u][1]]) ans[u] = 1;
	}
	rep(u,1,n){
		if(!ans[u]) printf("B");
		else printf("R");
	}
	printf("\n");
}

int main(){	
//	freopen("test.in","r",stdin);
	scanf("%d",&T);
	while(T--) solve();
	return 0;
}