#include<bits/stdc++.h>
using namespace std;
constexpr int M=2e5+5;
int n,m,x,y,col[M];
vector<int>adj[M];
int read(){
    int x=0;char ch=getchar();
    while (!isdigit(ch)) ch=getchar();
    while (isdigit(ch)) x=x*10+ch-48,ch=getchar();
    return x;
}
void solve(){
    n=read();m=read();
    for (int i=1;i<=n;i++) col[i]=-1,adj[i].clear();
    for (int i=1;i<=m;i++){
        x=read()+1;y=read()+1;
        adj[x].push_back(y);
        adj[y].push_back(x);
    }
    for (int i=1;i<=n;i++)
        adj[i].push_back(i%n+1),
        adj[i%n+1].push_back(i);
    queue<int>q;q.push(1);col[1]=0;
    while (!q.empty()){
        int x=q.front();q.pop();
        for (auto y:adj[x])
            if (!~col[y])
                col[y]=!col[x],q.push(y);
    }
    for (int i=1;i<=n;i++) putchar(col[i]?'B':'R');puts("");
}
int main(){int T=read();while (T--) solve();return 0;}