#include <bits/stdc++.h>
using namespace std;

int n, m, deg[200005];
bool vis[200005];
vector<int> G[200005];
void adde(int u, int v) {
    G[u].push_back(v);
    G[v].push_back(u);
}

char S[200005];
void solve() {
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i++) G[i].clear();
    for(int i = 0; i < n; i++) adde(i % n + 1, (i + 1) % n + 1);
    for(int i = 0; i < m; i++) {
        int u, v;
        scanf("%d%d", &u, &v);
        G[u].push_back(v);
        G[v].push_back(u);
    }

    queue<int> que;
    for(int i = 1; i <= n; i++) if((deg[i] = G[i].size()) <= 2) {
        que.push(i); vis[i] = true;
    } else vis[i] = false;

    vector<int> seq;
    while(!que.empty()) {
        int v = que.front(); que.pop();
        seq.push_back(v);
        for(auto u : G[v]) if(!vis[u]) {
            deg[u]--;
            if(deg[u] <= 2) {
                vis[u] = true; que.push(u);
            }
        }
    }
    reverse(seq.begin(), seq.end());

    for(int i = 1; i <= n; i++) S[i] = ' ';
    for(auto v : seq) {
        for(auto u : G[v]) if(S[u] != ' ') S[v] = S[u] == 'R' ? 'B' : 'R';
        if(S[v] == ' ') S[v] = 'R';
    }
    printf("%s\n", S + 1);
}

int main() {
    int T;
    scanf("%d", &T);
    while(T--) solve();
    return 0;
}