#include<bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define pii pair<int, int>
void solve();

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int T = 1;
    cin >> T;
    while (T--)solve();
    return 0;
}
//const int mod = 998244353;

void solve()
{
    int n,m;
    cin>>n>>m;
    vector<vector<int>>g(n);
    int s=0;
    for(int i=1;i<=m;i++){
        int x,y;
        cin>>x>>y;
        g[x].push_back(y);
        g[y].push_back(x);
        s=x;
    }
    int ok=1;
    vector<int>ans(n),vis(n);
    for(int i=0;i<n;i++){
        int t=(i+s)%n;
        vis[t]=1;
        if(g[t].size()==0){
            ans[t]=ans[(t-1+n)%n]^1;
            continue;
        }
        for(int j:g[t]){
            if(vis[j])continue;
            ans[j]=ans[t]^1;
        }
    }
    for(int i=0;i<n;i++)cout<<(ans[i]==1 ? "B":"R");
    cout<<endl;
}