#include <bits/stdc++.h>
using namespace std;
#define V vector
#define all0(x) (x).begin(),(x).end()
#define all1(x) (x).begin()+1,(x).end()
#define pb push_back
#define fi first
#define se second
#define lb lower_bound
#define ub upper_bound
#define cin std::cin
#define cout std::cout
typedef long long LL;
typedef pair<int, int> pi;
typedef pair<LL, LL> pl;

//const int MN = 2e5 + 20;
const int INF = 2e9 + 1000;
const LL INFLL = 8e18 + 1000;
mt19937 mrand(chrono::steady_clock().now().time_since_epoch().count());
//模板区域~~~~~~~

//模板结束~~~~~~~

void solve() {
    int n, m; cin >> n >> m;
    V<V<int>> e(n);
    auto MOD = [&](int x) {
        while(x >= n) x -= n;
        while(x < 0) x += n;
        return x;
    };
    auto st = [&](int & x, int & y) {
        if(MOD(y - x) < MOD(x - y)) swap(x, y); 
    };
    V<pi> E(m + 1);
    for(int i = 1; i <= m; i++) {
        int x, y; cin >> x >> y;
        st(x, y);
        E[i] = {x, y};
    }
    sort(all1(E), [&](pi a, pi b) {
        return MOD(a.se - a.fi) < MOD(b.se - b.fi);
    });
    V<int> nxt(n);
    for(int i = 0; i < n; i++) nxt[i] = MOD(i + 1);
    for(int i = 1; i <= m; i++) {
        auto [x, y] = E[i];
        nxt[x] = y;
    }
    for(int i = 0; i < n; i++) {
        e[i].pb(nxt[i]);
        e[nxt[i]].pb(i);
    }

    V<int> c(n), vis(n);
    auto dfs = [&](int x, auto dfs) -> void {
        vis[x] = 1;
        for(auto y : e[x]) {
            if(vis[y]) ;
            else {
                c[y] = c[x] ^ 1;
                dfs(y, dfs);
            }
        }
    };
    for(int i = 0; i < n; i++) {
        if(!vis[i]) dfs(i, dfs);
    }
    for(int i = 0; i < n; i++) cout << (c[i] ? 'R' : 'B');
    cout << endl;
}

int32_t main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--) 
    solve();
}