#include<iostream>
#include<cstring>
#include<vector>
#include<set>
#include<cassert>
#include<algorithm>
using namespace std;
using LL = long long;

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T;
    cin >> T;
    while(T--){
        int n, m;
        cin >> n >> m;
        vector<vector<int> > g(n);
        vector<pair<int, int> > edge(m);
        for(int i = 0; i < m; i++){
            int a, b;
            cin >> a >> b;
            g[a].push_back(b);
            g[b].push_back(a);
            edge[i] = {a, b};
        }
        for(int i = 0; i < n; i++){
            int a = i, b = (i + 1) % n;
            g[a].push_back(b);
            g[b].push_back(a);
            edge.push_back({a, b});
        }

        vector<int> color(n);

        vector<int> d(n);
        for(auto [a, b] : edge){
            d[a] += 1;
            d[b] += 1;
        }
        vector<bool> del(n);

        vector<int> v;

        for(int i = 0; i < n; i++){
            if (d[i] <= 2){
                del[i] = true;
                v.push_back(i);
            }
        }

        vector<int> order;
        while(!v.empty()){
            sort(v.begin(), v.end());
            int pos = 0;
            for(int i = 0; i < v.size(); i++){
                if ((v[i] + 1) % n != v[(i + 1) % v.size()]){
                    pos = (i + 1) % v.size();
                    break;
                }
            }
            rotate(v.begin(), v.begin() + pos, v.end());
            order.insert(order.end(), v.begin(), v.end());
            vector<int> nv;
            for(auto x : v){
                for(auto j : g[x]){
                    if (--d[j] <= 2 and !del[j]){
                        del[j] = true;
                        nv.push_back(j);
                    }
                }
            }
            v.swap(nv);
        }

        reverse(order.begin(), order.end());
        assert(order.size() == n);
        set<int> s;
        for(auto x : order){
            if (!s.empty()){
                auto it = s.lower_bound(x);
                if (it == s.end()) it = s.begin();
                color[x] = color[*it] ^ 1;
            }
            s.insert(x);
        }
        for(auto x : color) cout << (x ? 'R' : 'B');
        cout << '\n';
    }

}