#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rof(i,a,b) for(int i=(a);i>=(b);--i)
using namespace std;
const int Maxn=2e5;

int n,m,fa[Maxn+5],id[Maxn+5],col[Maxn+5];
vector<int> w[Maxn+5],qr[Maxn+5],v[Maxn+5];
map<int,int> mp[Maxn+5];
inline int Find(int x) {return fa[x]==x?x:fa[x]=Find(fa[x]);}
inline void Addedge(int a,int b) {v[a].push_back(b),v[b].push_back(a);}
inline void dfs(int x,int fa)
{
    int c0=0,c1=0;
    for(auto i:w[x]) if(col[i]!=-1) (col[i]?c1:c0)++;
    for(auto i:w[x]) if(col[i]==-1)
        {if(c0<=c1) col[i]=0,c0++; else col[i]=1,c1++;}
    for(auto y:v[x]) if(y!=fa) dfs(y,x);
}
inline void Solve()
{
    cin>>n>>m; For(i,1,n+1) fa[i]=i,col[i]=-1;
    For(i,1,m)
    {
        int a,b; cin>>a>>b; a++,b++; if(a>b) swap(a,b);
        qr[b].push_back(a);
    }
    For(i,1,n) sort(qr[i].begin(),qr[i].end(),greater<int>());
    int cur=0; For(i,1,n) for(auto j:qr[i])
    {
        ++cur; for(int k=Find(j+1);k<i;k=fa[k])
            w[cur].push_back(k),fa[k]=Find(k+1);
        w[cur].push_back(i),w[cur].push_back(j);
    }
    ++cur; for(int k=Find(1);k<=n;k=fa[k])
        w[cur].push_back(k),fa[k]=Find(k+1);
    For(i,1,m+1) sort(w[i].begin(),w[i].end(),greater<int>());
    iota(id+1,id+m+2,1);
    sort(id+1,id+m+2,[&](int a,int b){return w[a]<w[b];});
    For(i,1,m+1)
    {
        int sz=w[i].size(); For(j,0,sz-1)
        {
            int b=w[i][j],a=w[i][(j+1)%sz];
            if(b==a%n+1) continue; if(a>b) swap(a,b);
            if(!mp[a][b]) mp[a][b]=i; else Addedge(i,mp[a][b]);
        }
    } dfs(1,0);
    For(i,1,n) putchar(col[i]?'R':'B'); printf("\n");
    For(i,1,m) vector<int>().swap(w[i]),vector<int>().swap(v[i]);
    For(i,1,n) vector<int>().swap(qr[i]),mp[i].clear();
}

int main()
{
    // freopen("1.in","r",stdin);

    int T; cin>>T;
    while(T--) Solve();
    return 0;
}