#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define db double
#define pii pair<int,int>
#define pli pair<ll,int>
#define pil pair<int,ll>
#define pll pair<ll,ll>
#define ti3 tuple<int,int,int>
#define int128 __int128_t
#define pii128 pair<int128,int128>
const int inf = 1 << 30;
const ll linf = 1e18;
const db EPS = 1e-10;
const db pi = acos(-1);
template<class T> bool chmin(T& x, T y){
    if(x > y) {
        x = y;
        return true;
    } else return false;
}
template<class T> bool chmax(T& x, T y){
    if(x < y) {
        x = y;
        return true;
    } else return false;
}

// overload macro
#define CAT( A, B ) A ## B
#define SELECT( NAME, NUM ) CAT( NAME, NUM )

#define GET_COUNT( _1, _2, _3, _4, _5, _6 /* ad nauseam */, COUNT, ... ) COUNT
#define VA_SIZE( ... ) GET_COUNT( __VA_ARGS__, 6, 5, 4, 3, 2, 1 )

#define VA_SELECT( NAME, ... ) SELECT( NAME, VA_SIZE(__VA_ARGS__) )(__VA_ARGS__)

// rep(overload)
#define rep( ... ) VA_SELECT(rep, __VA_ARGS__)
#define rep2(i, n) for (int i = 0; i < int(n); i++)
#define rep3(i, a, b) for (int i = a; i < int(b); i++)
#define rep4(i, a, b, c) for (int i = a; i < int(b); i += c)

// repll(overload)
#define repll( ... ) VA_SELECT(repll, __VA_ARGS__)
#define repll2(i, n) for (ll i = 0; i < (ll)(n); i++)
#define repll3(i, a, b) for (ll i = a; i < (ll)(b); i++)
#define repll4(i, a, b, c) for (ll i = a; i < (ll)(b); i += c)

// rrep(overload)
#define rrep( ... ) VA_SELECT(rrep, __VA_ARGS__)    
#define rrep2(i, n) for (int i = n - 1; i >= 0; i--)
#define rrep3(i, a, b) for (int i = b - 1; i >= a; i--)
#define rrep4(i, a, b, c) for (int i = b - 1; i >= a; i -= c)

// rrepll(overload)
#define rrepll( ... ) VA_SELECT(rrepll, __VA_ARGS__)
#define rrepll2(i, n) for (ll i = (ll)(n) - 1; i >= 0ll; i--)
#define rrepll3(i, a, b) for (ll i = b - 1; i >= (ll)(a); i--)
#define rrepll4(i, a, b, c) for (ll i = b - 1; i >= (ll)(a); i -= c)

// for_earh
#define fore(e, v) for (auto&& e : v)

// vector
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()

template<class T, T(* op)(T, T), T(* e)()>
struct segment_tree{
    int N;
    vector<T> node;

    segment_tree(int n) {
        N = 1;
        while(N < n) N *= 2;
        node.resize(N * 2 - 1, e());
    }

    void update(int i, T x){
        i += N - 1;
        node[i] = x;
        while(i > 0){
            i = (i - 1) / 2;
            node[i] = op(node[i * 2 + 1], node[i * 2 + 2]);
        }
    }

    T get_val(int a, int b, int k = 0, int l = 0, int r = -1){
        if(r == -1) r = N;
        if(b <= l || r <= a) return e();
        if(a <= l && r <= b) return node[k];

        T vl = get_val(a, b, k * 2 + 1, l, (l + r) / 2);
        T vr = get_val(a, b, k * 2 + 2, (l + r) / 2, r);
        return op(vl, vr);
    }
};

int op(int a, int b) {
    return a + b;
}

int e() {
    return 0;
}

void solve() {
    int n, m;
    cin >> n >> m;
    vector<int> u(m), v(m);
    segment_tree<int, op, e> st(n);
    rep (i, m) {
        cin >> u[i] >> v[i];
        st.update(u[i], 1);
        st.update(v[i], 1);
        if (u[i] > v[i]) swap(u[i], v[i]);
    }

    string S(n, 'R');
    rep (i, m) {
        if (st.get_val(u[i] + 1, v[i]) == 0) {
            S[u[i] + 1] = 'B';
        } else {
            S[(u[i] - 1 + n) % n] = 'B';
        }
    }
    if (m != 0) S[u[0]] = 'B';
    else S[0] = 'B';
    cout << S << '\n';
}

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    int t;
    cin >> t;
    while (t--) solve();
    return 0;
}