#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
template<typename T> using vec = vector<T>;

void solve()
{
    int n, m;
    cin >> n >> m;
    vec<vec<int>> g(n);
    for (int i = 0; i < n - 1; i++) {
        g[i].emplace_back(i + 1);
        g[i + 1].emplace_back(i);
    }
    g[0].emplace_back(n - 1);
    g[n - 1].emplace_back(0);
    while (m--) {
        int u, v;
        cin >> u >> v;
        g[u].emplace_back(v);
        g[v].emplace_back(u);
    }
    vec<char> col(n + 1);
    auto dfs = [&](auto &&f, int x, int fa) -> void
    {
        col[x] = col[fa];
        for (int v: g[x]) if (v != fa) {
            if (col[v]) {
                col[x] = 3 - col[x];
                break;
            }
        }
        for (int v: g[x]) if (!col[v]) f(f, v, x);
    };
    col[n] = 1;
    dfs(dfs, 0, n);
    for (int i = 0; i < n; i++) {
        if (col[i] == 1) cout.put('R');
        else cout.put('B');
    }
    cout << '\n';
}

signed main()
{
    int t;
    cin >> t;
    while (t--) solve();
    return 0;
}