#include <bits/stdc++.h>

#define rep(i,s,n) for(int i = int(s); i < int(n); i++)
#define rrep(i,s,n) for(int i = int(n) - 1; i >= int(s); i--)
#define all(v) (v).begin(),(v).end()

using ll = long long;
using ld = long double;
using ull = unsigned long long;

bool chmin(auto &a, auto b) {
    if(a <= b) return false;
    a = b;
    return true;
}

bool chmax(auto &a, auto b) {
    if(a >= b) return false;
    a = b;
    return true;
}

using namespace std;

const int iinf = 1e9;

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &a){
    const char* delim = "";
    for (auto &x : a){
        os << exchange(delim," ") << x;
    }
    return os;
}

using pii = pair<int,int>;

vector<pii> preprocess(int n, int m){
    vector<ll> add(n,0), del(n,0);
    stack<int> st;
    vector<pii> ans;
    rep(i,0,m){
        int u, v; cin >> u >> v;
        if (u > v) swap(u,v);
        add[u]++, del[v]++;
    }
    set<pii> est;
    auto f = [&](int u, int v){
        est.insert(pii(u,v));
        est.insert(pii(v,u));
    };
    rep(i,0,n){
        rep(tt,0,del[i]){
            while (true){
                ll pre = st.top(); st.pop();
                f(i,pre%n);
                pre -= n;
                if (pre >= 0){
                    st.push(pre);
                    break;
                }
            }
        }
        st.push(add[i]*n+i);
    }
    while (!st.empty()){
        f(0,st.top()); st.pop();
    }
    rep(i,0,n){
        f(i, i == n-1 ? 0 : i+1);
        f(i, i == 0 ? n-1 : i-1);
    }
    for (auto [u, v] : est){
        ans.emplace_back(u,v);
        if (u < v){
            // cerr << u << ' ' << v << endl;
        }
    }
    return ans;
}

void solve(){
    int n, m; cin >> n >> m;
    vector<set<int>> g(n);
    auto es = preprocess(n,m);
    for (auto [u, v] : es){
        g[u].insert(v);
    }
    auto deg = [&](int v){
        return g[v].size();
    };
    vector<int> ans(n,0);
    auto dfs = [&](auto sfs, set<int> del) -> void {
        set<int> deg2;
        vector<int> ops;
        for (int v : del){
            // deg(v) == 2
            int op = -1;
            for (int u : g[v]){
                if (del.contains(u)) continue;
                g[u].erase(v);
                if (deg(u) == 2){
                    deg2.insert(u);
                }
                op = u;
            }
            ops.emplace_back(op);
        }
        if (deg2.empty()){
            // del.size() >= 2
            int x = 0;
            for (int v : del){
                ans[v] = x;
                x ^= 1;
            }
            return ;
        }
        sfs(sfs,deg2);
        for (int i = 0; int v : del){
            if (ops[i] != -1){
                int u = ops[i];
                // cerr << "op " << v << " = " << u << endl;
                ans[v] = ans[u] ^ 1;
            }
            i++;
        }
    };
    set<int> deg2;
    rep(i,0,n){
        if (deg(i) == 2){
            deg2.insert(i);
        }
    }
    dfs(dfs,deg2);
    string sans = "";
    rep(i,0,n) sans += (ans[i] == 0 ? 'B' : 'R');
    cout << sans << '\n';
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    int t; cin >> t;
    while (t--){
        solve();
    }
}