#include<bits/stdc++.h>
#define rep(i, a, b) for(int i = a; i <= b; i++)
#define per(i, a, b) for(int i = a; i >= b; i--)
#define int long long
#define RD read()
#define PN putchar('\n')
using namespace std;
inline int read() {
    int x = 0, f = 1;
    char ch = getchar();
    while(ch < '0' || ch > '9') { if(ch == '-') f = -1; ch = getchar(); }
    while('0' <= ch && ch <= '9') { x = (x << 1) + (x << 3) + (ch ^ 48); ch = getchar(); }
    return x * f;
}
int const N = 2e5 + 5;
int n, m;
set<int> s[N];
#define pii pair<int, int>
set<pii> q;
int ans[N];
void solve(int step) {
    // printf("\nsolve step = %lld\n", step);
    if(step == n - 1) {
        int x = (*q.begin()).second, y = (*--q.end()).second;
        ans[x] = 1, ans[y] = 1;
        return;
    }
    int x = (*q.begin()).second; q.erase(q.begin());
    int a = *s[x].begin(), b = *--s[x].end();
    // printf("x = %lld, a = %lld, b = %lld\n", x, a, b);
    // for(int y : s[x]) printf("%lld ", y); PN;
    if(s[a].find(b) == s[a].end()) {
        s[a].insert(b), s[b].insert(a);
    } else {
        auto xa = q.find({s[a].size(), a}), xb = q.find({s[b].size(), b});
        auto va = *xa, vb = *xb;
        q.erase(xa), q.erase(xb);
        q.insert({va.first - 1, va.second}), q.insert({vb.first - 1, vb.second});
    }
    s[a].erase(x), s[b].erase(x);

    solve(step + 1);

    // printf("\nback to %lld\n", x);
    // printf("l = %lld, ansl = %lld, r = %lld, ansr = %lld\n", a, ans[a], b, ans[b]);
    if(ans[a] == ans[b]) ans[x] = !ans[a];
    else ans[x] = 1;
}
#define DEBUG 1
signed main() {
    int T = RD;
    while(T --) {
        n = RD, m = RD;
        rep(i, 1, n) s[i].clear();
        rep(i, 1, m) {
            int u = RD + DEBUG, v = RD + DEBUG;
            s[u].insert(v);
            s[v].insert(u);
        }
        rep(i, 1, n - 1) { 
            s[i].insert(i + 1);
            s[i + 1].insert(i);
        }
        s[n].insert(1);
        s[1].insert(n);

        // rep(i, 1, n) {
        //     printf("set %lld:", i);
        //     for(int x : s[i]) printf("%lld ", x); PN;
        // }

        q.clear();
        rep(i, 1, n) q.insert({s[i].size(), i});

        solve(1);

        rep(i, 1, n) printf("%c", ans[i] ? 'R' : 'B'); PN;
    }
    return 0;
}
/*
1
7 2
2 5
1 5
*/