#include<bits/stdc++.h>
#define int long long
#define pii pair<int, int>
#define ll long long
using namespace std;
const int maxn = 2e5 + 10;
vector<int> G[maxn];
int fa[maxn], col[maxn];
int Find(int x) {return fa[x] == x ? fa[x] : fa[x] = Find(fa[x]);}
void dfs(int u, int f) {
    for (auto v : G[u]) {
        if (v == f) continue;
        col[v] = col[u] ^ 1;
        dfs(v, u);
    }
}
void solve() {
    int n, m; cin >> n >> m;
    for (int i = 0; i < n; i++) fa[i] = i, G[i].clear();
    while (m--) {
        int u, v; cin >> u >> v;
        int fu = Find(u), fv = Find(v);
        if (fu == fv) continue;
        fa[fu] = fv;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    for (int i = 0; i < n; i++) {
        int u = i, v = (i + 1) % n;
        int fu = Find(u), fv = Find(v);
        if (fu == fv) continue;
        fa[fu] = fv;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    col[0] = 0;
    dfs(0, 0);
    for (int i = 0; i < n; i++)
        if (col[i]) cout << 'B';
        else cout << 'R';
    cout << "\n";
}
signed main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--) solve();
    return 0;
}