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

void solve() {
  int n, m;
  cin >> n >> m;
  vector<vector<int>> adj(n);
  for (int i = 0; i < m; ++i) {
    int u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  vector<int> col(n, -1);
  auto dfs = [&](auto self, int u, int c)->void {
    col[u] = c;
    for (auto v : adj[u]) {
      if (~col[v]) continue;
      self(self, v, c ^ 1);
    }
  };
  for (int i = 0; i < n; ++i) {
    if (adj[i].size() && col[i] == -1)
      dfs(dfs, i, 0);
  }
  if (!m) {
    for (int i = 0; i < n; ++i)
      col[i] = i % 2;
  } else {
    for (int i = 0; i < n; ++i) {
      if (col[i] == -1) continue;
      int c = col[i];
      for (int j = (i + 1) % n; col[j] == -1; j = (j + 1) % n)
        col[j] = (c ^= 1);
    }
  }
  for (int i = 0; i < n; ++i)
    cout << (col[i] == 0 ? 'R' : 'B');
  cout << "\n";
}

int main() {
  cin.tie(0)->sync_with_stdio(0);
  int t;
  cin >> t;
  while (t--)
    solve();
  return 0;
}