#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define int long long
using i64 = long long;
using i128 = __int128;
using f64 = double;
using f128 = long double;
constexpr i64 mod = [](bool n) { return n ? 998244353 : 1e9 + 7; } (1);
mt19937_64 rd(chrono::steady_clock::now().time_since_epoch().count());
template <class K, class C = less<>> using paring_heap = __gnu_pbds::priority_queue<K, C>;
template <class K> using rb_tree = tree<K, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update>;
ostream & operator << (ostream & os, i128 t) {
    if (t == 0) os << 0;
    if (t < 0) t = -t, os << '-';
    string s;
    for (; t; s += '0' + t % 10, t /= 10);
    return reverse(s.begin(), s.end()), os << s;
}
template <class T, class ... A> void debug(T t, A ... a) { cerr << "[" << t, ((cerr << ", " << a), ...), cerr << "]\n"; }

void QAQ() {
    int n, m;
    cin >> n >> m;

    vector adj(n + 1, vector<int>());

    for (int i = 0, u, v; i < m; i++) {
        cin >> u >> v;
        u++, v++;
        adj[u].emplace_back(v), adj[v].emplace_back(u);
    }

    vector<char> ans(n + 1, ' ');

    for (int i = 1; i <= n; i++) {
        if (ans[i] == ' ') {
            auto dfs = [&](auto && self, int u) -> void {
                set<char> t;
                for (auto & v : adj[u]) {
                    if (ans[v] != ' ') {
                        t.insert(ans[v]);
                    }
                }
                if (t.size() == 0) {
                    ans[u] = 'B';
                } else if (t.size() == 1) {
                    if (*t.begin() == 'B') {
                        ans[u] = 'R';
                    } else {
                        ans[u] = 'B';
                    }
                } else {
                    ans[u] = 'R';
                    for (auto & v : adj[u]) {
                        if (ans[v] == ' ') {
                            self(self, v);
                        }
                    }
                }
            };

            dfs(dfs, i);
        }
    }

    if (m == 0) {
        ans[1] = 'R';
    }

    for (int i = 1; i <= n; i++) {
        cout << ans[i];
    }
    cout << "\n";
}

signed main() {
    cin.tie(0) -> sync_with_stdio(0);
    int t = 1;
    cin >> t;
    for (cout << fixed << setprecision(12); t--; QAQ());
}