#include <bits/stdc++.h>
using namespace std;

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<pii> vpii;
typedef complex<double> cpx;
template <typename T> using minPq = priority_queue<T, vector<T>, greater<T>>;
#define ms(a, x) memset(a, x, sizeof(a))
#define pb push_back
#define fs first
#define sn second
#define ALL(v) begin(v), end(v)
#define SZ(v) ((int) (v).size())
#define lbv(v, x) (lower_bound(ALL(v), x) - (v).begin())
#define ubv(v, x) (upper_bound(ALL(v), x) - (v).begin())
template <typename T> inline void UNIQUE(vector<T> &v){sort(ALL(v)); v.resize(unique(ALL(v)) - v.begin());}
const int INF = 0x3f3f3f3f;
const ll LLINF = 0x3f3f3f3f3f3f3f3f;
const double PI = acos(-1);
#define FR(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define FORR(i, a, b) for(int i = (a); i >= (b); i--)
#define dbg(x) {cerr << #x << ' ' << x << endl;}
#define dbgArr(arr, n) {cerr << #arr; FR(_i, n) cerr << ' ' << (arr)[_i]; cerr << endl;}
template <typename T, typename U>
ostream& operator<<(ostream &os, pair<T, U> p){return os << "(" << p.fs << ", " << p.sn << ")";}

const int MN = 2e5 + 5;
int n, m;
pii edges[MN];
vi vecs[MN];
set<int> st;
bool ans[MN];

void solve(){
    cin >> n >> m;
    FR(i, m){
        int a, b;
        cin >> a >> b;
        if(b < a) swap(a, b);
        edges[i] = {a, b};
    }
    sort(edges, edges+m, [](pii a, pii b){return a.sn-a.fs < b.sn-b.fs;});
    FR(i, n) st.insert(i);

    FR(i, m){
        auto [a, b] = edges[i];
        for(auto it = st.upper_bound(a); *it < b; it = st.erase(it)) vecs[i].pb(*it);
        assert(!vecs[i].empty());
    }

    assert(SZ(st) >= 3);
    bool c = 0;
    for(int a : st) ans[a] = c ^= 1;

    FORR(i, m-1, 0){
        for(int a : vecs[i]) ans[a] = !ans[edges[i].fs];
    }
}

int main(){
    cin.sync_with_stdio(0); cin.tie(0);
    int t; cin >> t;
    while(t--){
        solve();
        FR(i, n) cout << "BR"[ans[i]];
        cout << '\n';

        FR(i, m) vecs[i].clear();
        st.clear();
        FR(i, n) ans[i] = 0;
    }
}