#include <bits/stdc++.h>
#define dd(x) cout << #x << "\n"
#define d(x) cout << #x  << ": " << x << "\n"
using namespace std;
#define int long long
using pii = pair<int, int>;
using vpii = vector<pii>;
using vi = vector<int>;
using vii = vector<vector<int>>;
using a3 = array<int, 3>;
const int inf = 0x3f3f3f3f3f3f3f3fLL;

void solve() {
    int n, m; cin >> n >> m;
    set<int> s;
    vector<int> col(n);
    fill(col.begin(), col.end(), -1);
    for(int i = 1; i <= m; i++) {
        int u, v; cin >> u >> v;
        s.insert(u); s.insert(v);
    }
    
    s.insert(0); s.insert(1);
    int now = 0;
    for(auto it : s) {
        col[it] = now;
        now = !now;
    }

    int st = *s.begin();
    for(int i = st + 1; i < n; i++) {
        if(col[i] == -1) {
            col[i] = !col[i - 1];
        }
    }

    if(~col[0]) col[0] = !col[n];
    for(int i = 1; i < st; i++) {
        if(!col[i]) {
            col[i] = !col[i - 1];
        }
    }

    for(int i = 0; i < n; i++) {
        cout << (col[i] ? "R" : "B");
    }
    cout << "\n";
}

signed main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int T; cin >> T;
    while(T--) solve();
    return 0;
}

/*
3
3 0

4 1
1 3

6 3
0 2
2 4
4 0
*/