#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define x first
#define y second

void solve();

int main() {
#ifndef LOCAL
	cin.tie(nullptr)->sync_with_stdio(false);
#endif
	cout << fixed << setprecision(30);
	int t = 1;
	cin >> t;
	while (t--) {
		solve();
	}
}


void solve() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>> g(n);
	for (int i = 0; i < m; ++i) {
		int x, y;
		cin >> x >> y;
		g[x].push_back(x);
		g[y].push_back(x);
	}
	for (int i = 0; i < n; ++i) {
		int j = (i + 1) % n;
		g[i].push_back(j);
		g[j].push_back(i);
	}
	vector<int> deg(n);
	for (int i = 0; i < n; ++i) deg[i] = g[i].size();
	set<pair<int, int>> st;
	for (int i = 0; i < n; ++i) {
		st.emplace(deg[i], i);
	}
	vector<bool> used(n);
	string ans(n, '#');
	auto go = [&](auto go) -> void {
		if (st.empty()) return;
		int u = st.begin()->second;
		st.erase(st.begin());
		used[u] = true;
		vector<int> vert;
		for (auto to : g[u]) {
			if (!used[to]) {
				st.erase({deg[to], to});
				vert.push_back(to), deg[to]--;
				st.emplace(deg[to], to);
			}
		}
		go(go);
		if (vert.size() == 0) {
			ans[u] = 'R';
		} else {
			ans[u] = 'B' + 'R' - ans[vert[0]];
		}
	};
	go(go);
	cout << ans << '\n';
}