#line 1 "C.cpp"
// #pragma GCC target("avx2,avx512f,avx512vl,avx512bw,avx512dq,avx512cd,avx512vbmi,avx512vbmi2,avx512vpopcntdq,avx512bitalg,bmi,bmi2,lzcnt,popcnt")
// #pragma GCC optimize("Ofast")

#line 2 "/mnt/c/Users/tsigm/Documents/Cprogram/library/template.hpp"

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb push_back
#define eb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> bool chmax(T& x, U y){
	if(x<y){ x=y; return true; }
	return false;
}
template<class T,class U> bool chmin(T& x, U y){
	if(y<x){ x=y; return true; }
	return false;
}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class T> int lwb(const V<T>& v, const T& a){return lower_bound(all(v),a) - v.begin();}
template<class T>
V<T> Vec(size_t a) {
    return V<T>(a);
}
template<class T, class... Ts>
auto Vec(size_t a, Ts... ts) {
  return V<decltype(Vec<T>(ts...))>(a, Vec<T>(ts...));
}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

template<class D> D divFloor(D a, D b){
	return a / b - (((a ^ b) < 0 && a % b != 0) ? 1 : 0);
}
template<class D> D divCeil(D a, D b) {
	return a / b + (((a ^ b) > 0 && a % b != 0) ? 1 : 0);
}

/*
x       0  1  2  3  4  5  6  7  8  9
bsr(x) -1  0  1  1  2  2  2  2  3  3
最上位bit
*/
int bsr(int x){
	return x == 0 ? -1 : 31 ^ __builtin_clz(x);
}
int bsr(uint x){
	return x == 0 ? -1 : 31 ^ __builtin_clz(x);
}
int bsr(ll x){
	return x == 0 ? -1 : 63 ^ __builtin_clzll(x);
}
int bsr(ull x){
	return x == 0 ? -1 : 63 ^ __builtin_clzll(x);
}

/*
x       0  1  2  3  4  5  6  7  8  9
bsl(x) -1  0  1  0  2  0  1  0  3  0
最下位bit
*/
int bsl(int x){
	if(x==0) return -1;
	return __builtin_ctz(x);
}
int bsl(uint x){
	if(x==0) return -1;
	return __builtin_ctz(x);
}
int bsl(ll x){
	if(x==0) return -1;
	return __builtin_ctzll(x);
}
int bsl(ull x){
	if(x==0) return -1;
	return __builtin_ctzll(x);
}


template<class T>
T rnd(T l,T r){	//[l,r)
	using D = uniform_int_distribution<T>;
	static random_device rd;
	static mt19937 gen(rd());
	return D(l,r-1)(gen);
}
template<class T>
T rnd(T n){	//[0,n)
	return rnd(T(0),n);
}
#line 5 "C.cpp"

void solve(){
	int N,M; cin >> N >> M;
	VV<int> G(N);
	rep(i,N){
		int j = (i+1)%N;
		G[i].eb(j); G[j].eb(i);
	}
	rep(i,M){
		int x,y; cin >> x >> y;
		G[x].eb(y); G[y].eb(x);
	}
	rep(i,N) sort(all(G[i]));
	V<int> col(N,-1);
	auto dfs = [&](auto&& self, int l, int r) -> void {
		if(r-l <= 1){
			return;
		}
		assert(col[l] != -1 && col[r] != -1);
		assert(col[l] != col[r]);
		V<int> vs;
		for(auto v: G[r]) if(l <= v && v < r){
			vs.eb(v);
		}
		int K = si(vs);
		rep(i,K) col[vs[i]] = col[l] ^ (i%2);
		rep(i,K-1){
			self(self,vs[i],vs[i+1]);
		}
	};
	{
		col[0] = 0;
		V<int> vs = G[0];
		int K = si(vs);
		rep(i,K) col[vs[i]] = i%2;
		rep(i,K-1) dfs(dfs,vs[i],vs[i+1]);
	}
	show(col);
	rep(i,N) cout << (col[i] ? 'B' : 'R');
	cout << '\n';
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	int T; cin >> T;
	while(T--) solve();
}