#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
const int N = 3e5 + 5;
const int mod = 1e9 + 5;
int n, m;

vector<ll> v[200005];
ll co[200005];
bool vis[1000005];
void bfs(ll x) {
    queue<ll> q;
    for (auto i : v[x]) {
        q.push(i);
        co[i] = 1;
        vis[i] = 1;
    }
    while (!q.empty()) {
        ll nxt = q.front();
        q.pop();
        for (auto i : v[nxt]) {
            if (vis[i])continue;
            co[i] = co[nxt] ^ 1;
            vis[i] = 1;
            q.push(nxt);
        }
    }
}
void solve()
{
    cin >> n >> m;
    for (int i = 0;i < n;i++) {
        vis[i] = 0;
        co[i] = 0;
        v[i].clear();
    }
    for (int i = 0;i < n;i++) {
        if (i < n - 1)
            
            v[i].push_back(i + 1);
        if (i > 0)
            
            v[i].push_back(i - 1);
    }
    v[0].push_back(n-1);
    v[n-1].push_back(0);
    for (int i = 0;i < m;i++) {
        ll x, y;
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    co[1] = 0;
    vis[1] = 1;
    bfs(1);
    for (int i = 0;i < n;i++) {
        if (co[i]) cout << "B";
        else cout << "R";
    }
    cout << "\n";
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}