/**
 * date   : 2024-04-13 15:30:02
 * author : Nyaan
 */

#define NDEBUG

using namespace std;

// intrinstic
#include <immintrin.h>

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <typeinfo>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

// utility

namespace Nyaan {
using ll = long long;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;

template <typename T>
using V = vector<T>;
template <typename T>
using VV = vector<vector<T>>;
using vi = vector<int>;
using vl = vector<long long>;
using vd = V<double>;
using vs = V<string>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<long long>>;
template <typename T>
using minpq = priority_queue<T, vector<T>, greater<T>>;

template <typename T, typename U>
struct P : pair<T, U> {
  template <typename... Args>
  P(Args... args) : pair<T, U>(args...) {}

  using pair<T, U>::first;
  using pair<T, U>::second;

  P &operator+=(const P &r) {
    first += r.first;
    second += r.second;
    return *this;
  }
  P &operator-=(const P &r) {
    first -= r.first;
    second -= r.second;
    return *this;
  }
  P &operator*=(const P &r) {
    first *= r.first;
    second *= r.second;
    return *this;
  }
  template <typename S>
  P &operator*=(const S &r) {
    first *= r, second *= r;
    return *this;
  }
  P operator+(const P &r) const { return P(*this) += r; }
  P operator-(const P &r) const { return P(*this) -= r; }
  P operator*(const P &r) const { return P(*this) *= r; }
  template <typename S>
  P operator*(const S &r) const {
    return P(*this) *= r;
  }
  P operator-() const { return P{-first, -second}; }
};

using pl = P<ll, ll>;
using pi = P<int, int>;
using vp = V<pl>;

constexpr int inf = 1001001001;
constexpr long long infLL = 4004004004004004004LL;

template <typename T>
int sz(const T &t) {
  return t.size();
}

template <typename T, typename U>
inline bool amin(T &x, U y) {
  return (y < x) ? (x = y, true) : false;
}
template <typename T, typename U>
inline bool amax(T &x, U y) {
  return (x < y) ? (x = y, true) : false;
}

template <typename T>
inline T Max(const vector<T> &v) {
  return *max_element(begin(v), end(v));
}
template <typename T>
inline T Min(const vector<T> &v) {
  return *min_element(begin(v), end(v));
}
template <typename T>
inline long long Sum(const vector<T> &v) {
  return accumulate(begin(v), end(v), 0LL);
}

template <typename T>
int lb(const vector<T> &v, const T &a) {
  return lower_bound(begin(v), end(v), a) - begin(v);
}
template <typename T>
int ub(const vector<T> &v, const T &a) {
  return upper_bound(begin(v), end(v), a) - begin(v);
}

constexpr long long TEN(int n) {
  long long ret = 1, x = 10;
  for (; n; x *= x, n >>= 1) ret *= (n & 1 ? x : 1);
  return ret;
}

template <typename T, typename U>
pair<T, U> mkp(const T &t, const U &u) {
  return make_pair(t, u);
}

template <typename T>
vector<T> mkrui(const vector<T> &v, bool rev = false) {
  vector<T> ret(v.size() + 1);
  if (rev) {
    for (int i = int(v.size()) - 1; i >= 0; i--) ret[i] = v[i] + ret[i + 1];
  } else {
    for (int i = 0; i < int(v.size()); i++) ret[i + 1] = ret[i] + v[i];
  }
  return ret;
};

template <typename T>
vector<T> mkuni(const vector<T> &v) {
  vector<T> ret(v);
  sort(ret.begin(), ret.end());
  ret.erase(unique(ret.begin(), ret.end()), ret.end());
  return ret;
}

template <typename F>
vector<int> mkord(int N, F f) {
  vector<int> ord(N);
  iota(begin(ord), end(ord), 0);
  sort(begin(ord), end(ord), f);
  return ord;
}

template <typename T>
vector<int> mkinv(vector<T> &v) {
  int max_val = *max_element(begin(v), end(v));
  vector<int> inv(max_val + 1, -1);
  for (int i = 0; i < (int)v.size(); i++) inv[v[i]] = i;
  return inv;
}

vector<int> mkiota(int n) {
  vector<int> ret(n);
  iota(begin(ret), end(ret), 0);
  return ret;
}

template <typename T>
T mkrev(const T &v) {
  T w{v};
  reverse(begin(w), end(w));
  return w;
}

template <typename T>
bool nxp(T &v) {
  return next_permutation(begin(v), end(v));
}

// 返り値の型は入力の T に依存
// i 要素目 : [0, a[i])
template <typename T>
vector<vector<T>> product(const vector<T> &a) {
  vector<vector<T>> ret;
  vector<T> v;
  auto dfs = [&](auto rc, int i) -> void {
    if (i == (int)a.size()) {
      ret.push_back(v);
      return;
    }
    for (int j = 0; j < a[i]; j++) v.push_back(j), rc(rc, i + 1), v.pop_back();
  };
  dfs(dfs, 0);
  return ret;
}

// F : function(void(T&)), mod を取る操作
// T : 整数型のときはオーバーフローに注意する
template <typename T>
T Power(T a, long long n, const T &I, const function<void(T &)> &f) {
  T res = I;
  for (; n; f(a = a * a), n >>= 1) {
    if (n & 1) f(res = res * a);
  }
  return res;
}
// T : 整数型のときはオーバーフローに注意する
template <typename T>
T Power(T a, long long n, const T &I = T{1}) {
  return Power(a, n, I, function<void(T &)>{[](T &) -> void {}});
}

template <typename T>
T Rev(const T &v) {
  T res = v;
  reverse(begin(res), end(res));
  return res;
}

template <typename T>
vector<T> Transpose(const vector<T> &v) {
  using U = typename T::value_type;
  int H = v.size(), W = v[0].size();
  vector res(W, T(H, U{}));
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      res[j][i] = v[i][j];
    }
  }
  return res;
}

template <typename T>
vector<T> Rotate(const vector<T> &v, int clockwise = true) {
  using U = typename T::value_type;
  int H = v.size(), W = v[0].size();
  vector res(W, T(H, U{}));
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (clockwise) {
        res[W - 1 - j][i] = v[i][j];
      } else {
        res[j][H - 1 - i] = v[i][j];
      }
    }
  }
  return res;
}

}  // namespace Nyaan


// bit operation

namespace Nyaan {
__attribute__((target("popcnt"))) inline int popcnt(const u64 &a) {
  return __builtin_popcountll(a);
}
inline int lsb(const u64 &a) { return a ? __builtin_ctzll(a) : 64; }
inline int ctz(const u64 &a) { return a ? __builtin_ctzll(a) : 64; }
inline int msb(const u64 &a) { return a ? 63 - __builtin_clzll(a) : -1; }
template <typename T>
inline int gbit(const T &a, int i) {
  return (a >> i) & 1;
}
template <typename T>
inline void sbit(T &a, int i, bool b) {
  if (gbit(a, i) != b) a ^= T(1) << i;
}
constexpr long long PW(int n) { return 1LL << n; }
constexpr long long MSK(int n) { return (1LL << n) - 1; }
}  // namespace Nyaan


// inout

namespace Nyaan {

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.first << " " << p.second;
  return os;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
  is >> p.first >> p.second;
  return is;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  int s = (int)v.size();
  for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
  return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (auto &x : v) is >> x;
  return is;
}

istream &operator>>(istream &is, __int128_t &x) {
  string S;
  is >> S;
  x = 0;
  int flag = 0;
  for (auto &c : S) {
    if (c == '-') {
      flag = true;
      continue;
    }
    x *= 10;
    x += c - '0';
  }
  if (flag) x = -x;
  return is;
}

istream &operator>>(istream &is, __uint128_t &x) {
  string S;
  is >> S;
  x = 0;
  for (auto &c : S) {
    x *= 10;
    x += c - '0';
  }
  return is;
}

ostream &operator<<(ostream &os, __int128_t x) {
  if (x == 0) return os << 0;
  if (x < 0) os << '-', x = -x;
  string S;
  while (x) S.push_back('0' + x % 10), x /= 10;
  reverse(begin(S), end(S));
  return os << S;
}
ostream &operator<<(ostream &os, __uint128_t x) {
  if (x == 0) return os << 0;
  string S;
  while (x) S.push_back('0' + x % 10), x /= 10;
  reverse(begin(S), end(S));
  return os << S;
}

void in() {}
template <typename T, class... U>
void in(T &t, U &...u) {
  cin >> t;
  in(u...);
}

void out() { cout << "\n"; }
template <typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u) {
  cout << t;
  if (sizeof...(u)) cout << sep;
  out(u...);
}

struct IoSetupNya {
  IoSetupNya() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
    cerr << fixed << setprecision(7);
  }
} iosetupnya;

}  // namespace Nyaan


// debug


#ifdef NyaanDebug
#define trc(...) (void(0))
#else
#define trc(...) (void(0))
#endif

#ifdef NyaanLocal
#define trc2(...) (void(0))
#else
#define trc2(...) (void(0))
#endif


// macro

#define each(x, v) for (auto&& x : v)
#define each2(x, y, v) for (auto&& [x, y] : v)
#define all(v) (v).begin(), (v).end()
#define rep(i, N) for (long long i = 0; i < (long long)(N); i++)
#define repr(i, N) for (long long i = (long long)(N)-1; i >= 0; i--)
#define rep1(i, N) for (long long i = 1; i <= (long long)(N); i++)
#define repr1(i, N) for (long long i = (N); (long long)(i) > 0; i--)
#define reg(i, a, b) for (long long i = (a); i < (b); i++)
#define regr(i, a, b) for (long long i = (b)-1; i >= (a); i--)
#define fi first
#define se second
#define ini(...)   \
  int __VA_ARGS__; \
  in(__VA_ARGS__)
#define inl(...)         \
  long long __VA_ARGS__; \
  in(__VA_ARGS__)
#define ins(...)      \
  string __VA_ARGS__; \
  in(__VA_ARGS__)
#define in2(s, t)                           \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i]);                         \
  }
#define in3(s, t, u)                        \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i], u[i]);                   \
  }
#define in4(s, t, u, v)                     \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i], u[i], v[i]);             \
  }
#define die(...)             \
  do {                       \
    Nyaan::out(__VA_ARGS__); \
    return;                  \
  } while (0)


namespace Nyaan {
void solve();
}
int main() { Nyaan::solve(); }


//



using namespace std;




using namespace std;




using namespace std;

namespace internal {
unsigned long long non_deterministic_seed() {
  unsigned long long m =
      chrono::duration_cast<chrono::nanoseconds>(
          chrono::high_resolution_clock::now().time_since_epoch())
          .count();
  m ^= 9845834732710364265uLL;
  m ^= m << 24, m ^= m >> 31, m ^= m << 35;
  return m;
}
unsigned long long deterministic_seed() { return 88172645463325252UL; }

// 64 bit の seed 値を生成 (手元では seed 固定)
// 連続で呼び出すと同じ値が何度も返ってくるので注意
// #define RANDOMIZED_SEED するとシードがランダムになる
unsigned long long seed() {
#if defined(NyaanLocal) && !defined(RANDOMIZED_SEED)
  return deterministic_seed();
#else
  return non_deterministic_seed();
#endif
}

}  // namespace internal



using namespace std;

namespace internal {
template <typename T>
using is_broadly_integral =
    typename conditional_t<is_integral_v<T> || is_same_v<T, __int128_t> ||
                               is_same_v<T, __uint128_t>,
                           true_type, false_type>::type;

template <typename T>
using is_broadly_signed =
    typename conditional_t<is_signed_v<T> || is_same_v<T, __int128_t>,
                           true_type, false_type>::type;

template <typename T>
using is_broadly_unsigned =
    typename conditional_t<is_unsigned_v<T> || is_same_v<T, __uint128_t>,
                           true_type, false_type>::type;

#define ENABLE_VALUE(x) \
  template <typename T> \
  constexpr bool x##_v = x<T>::value;

ENABLE_VALUE(is_broadly_integral);
ENABLE_VALUE(is_broadly_signed);
ENABLE_VALUE(is_broadly_unsigned);
#undef ENABLE_VALUE

#define ENABLE_HAS_TYPE(var)                                   \
  template <class, class = void>                               \
  struct has_##var : false_type {};                            \
  template <class T>                                           \
  struct has_##var<T, void_t<typename T::var>> : true_type {}; \
  template <class T>                                           \
  constexpr auto has_##var##_v = has_##var<T>::value;

#define ENABLE_HAS_VAR(var)                                     \
  template <class, class = void>                                \
  struct has_##var : false_type {};                             \
  template <class T>                                            \
  struct has_##var<T, void_t<decltype(T::var)>> : true_type {}; \
  template <class T>                                            \
  constexpr auto has_##var##_v = has_##var<T>::value;

}  // namespace internal


namespace internal {
// 整数, 整数列を 64 bit unsigned int へ移す

using u64 = unsigned long long;
using u128 = __uint128_t;

ENABLE_HAS_TYPE(first_type);
ENABLE_HAS_TYPE(second_type);
ENABLE_HAS_TYPE(iterator);

template <typename T>
u64 hash_function(const T& x) {
  static u64 r = seed();
  constexpr u64 z1 = 11995408973635179863ULL;
  if constexpr (is_broadly_integral_v<T>) {
    // Integral
    return (u64(x) ^ r) * z1;
  } else if constexpr (has_first_type_v<T> && has_second_type_v<T>) {
    // pair
    constexpr u64 z2 = 10150724397891781847ULL;
    return hash_function(x.first) + hash_function(x.second) * z2;
  } else if constexpr (has_iterator_v<T>) {
    // Container
    constexpr u64 mod = (1LL << 61) - 1;
    constexpr u64 base = 950699498548472943ULL;
    u64 m = 0;
    for (auto& z : x) {
      u64 w;
      if constexpr (is_broadly_integral_v<T>) {
        w = u64(z) ^ r;
      } else {
        w = hash_function(z);
      }
      u128 y = u128(m) * base + (w & mod);
      m = (y & mod) + (y >> 61);
      if (m >= mod) m -= mod;
    }
    m ^= m << 24, m ^= m >> 31, m ^= m << 35;
    return m;
  } else {
    static_assert([]() { return false; }());
  }
}

template <typename Key>
struct HashObject {
  size_t operator()(const Key& x) const { return hash_function(x); }
};

}  // namespace internal

/*
@brief ハッシュ関数
*/

// 削除不可能な hashmap
//
// テンプレート引数
// fixed_size : これを true にするするとバケットサイズが固定になる
// get_hash : ハッシュ関数の指定
// 引数
// _default_value : val の初期値, この値で初期化
// _default_size :
// バケットサイズ, max(4, _default_size) 以上の 2 べきで初期化
// ただし fixed_size が true の時にしかサイズを変更できない

template <typename Key, typename Val, bool fixed_size = false,
          unsigned long long (*get_hash)(const Key&) =
              internal::hash_function<Key>>
struct UnerasableHashMap {
  int N, occupied_num, shift;
  vector<Key> keys;
  vector<Val> vals;
  vector<char> flag;

  Val default_value;
  int default_size;

  // サイズを n に変更する
  void init(int n, bool reset = false) {
    assert(n >= 4 && (n & (n - 1)) == 0);
    if constexpr (fixed_size) {
      assert(reset == true);
      n = N;
    }
    if (reset == true) {
      N = n, occupied_num = 0, shift = 64 - __builtin_ctz(n);
      keys.resize(n);
      vals.resize(n);
      flag.resize(n);
      fill(begin(vals), end(vals), default_value);
      fill(begin(flag), end(flag), 0);
    } else {
      N = n, shift = 64 - __builtin_ctz(n);
      vector<Key> keys2(n);
      vector<Val> vals2(n, default_value);
      vector<char> flag2(n);
      swap(keys, keys2), swap(vals, vals2), swap(flag, flag2);
      for (int i = 0; i < (int)flag2.size(); i++) {
        if (flag2[i]) {
          int j = hint(keys2[i]);
          keys[j] = keys2[i], vals[j] = vals2[i], flag[j] = 1;
        }
      }
    }
  }

  UnerasableHashMap(const Val& _default_value = Val{}, int _default_size = 4)
      : occupied_num(0), default_value(_default_value) {
    if (fixed_size == false) _default_size = 4;
    N = 4;
    while (N < _default_size) N *= 2;
    default_size = N;
    init(N, true);
  }

  int hint(const Key& k) {
    int hash = get_hash(k) >> shift;
    while (flag[hash] && keys[hash] != k) hash = (hash + 1) & (N - 1);
    return hash;
  }

  // key が i である要素への参照を返す
  Val& operator[](const Key& k) {
    int i = hint(k);
    if (!flag[i]) {
      if constexpr (fixed_size == false) {
        if (occupied_num * 2 >= N) {
          init(2 * N), i = hint(k);
        }
      }
      keys[i] = k, flag[i] = 1, occupied_num++;
    }
    return vals[i];
  }

  Val get(const Key& k) {
    int i = hint(k);
    return flag[i] ? vals[i] : default_value;
  }

  // 走査, f に関数 f(key, val) を入れる
  template <typename F>
  void enumerate(const F f) {
    for (int i = 0; i < (int)flag.size(); i++) {
      if (flag[i]) f(keys[i], vals[i]);
    }
  }

  int count(const Key& k) { return flag[hint(k)]; }
  bool contain(const Key& k) { return flag[hint(k)]; }
  int size() const { return occupied_num; }
  void reset() { init(default_size, true); }
  void clear() { init(default_size, true); }
};


using namespace Nyaan;

void q() {
  ini(N, M);

  vvi g(N);
  V<pi> st;
  vi visited;
  rep(i, N) {
    int j = (i + 1) % N;
    g[i].push_back(j);
    g[j].push_back(i);
    st.push_back(make_pair(i, j));
    st.push_back(make_pair(j, i));
  }
  {
    vl u(M), v(M);
    in2(u, v);
    rep(t, M) {
      int i = u[t], j = v[t];
      g[i].push_back(j);
      g[j].push_back(i);
      st.push_back(make_pair(i, j));
      st.push_back(make_pair(j, i));
    }
  }
  rep(i, N) sort(all(g[i]));
  sort(all(st));
  visited.resize(sz(st));

  vvi cv;
  rep(id, sz(st)) {
    if (visited[id]) continue;
    auto [u, v] = st[id];
    visited[id] = 1;
    vi c{u};
    for (int i = u, j = v; j != u;) {
      c.push_back(j);
      int z = lb(g[j], i);
      int k = g[j][(z + 1) % sz(g[j])];
      i = j, j = k;
      visited[lb<pi>(st, make_pair(i, j))] = 1;
    }
    if (c[0] != 0 or c[1] != 1) cv.push_back(c);
  }
  trc(cv);

  UnerasableHashMap<pi, vi> related;
  rep(i, sz(cv)) {
    rep(j, sz(cv[i])) {
      int u = cv[i][j];
      int v = cv[i][(j + 1) % sz(cv[i])];
      related[minmax(u, v)].push_back(i);
    }
  }

  vi used(sz(cv));
  string ans(N, ' ');
  queue<int> Q;

  auto add = [&](int i) {
    if (!used[i]) used[i] = 1, Q.push(i);
  };
  add(0);

  while (sz(Q)) {
    int i = Q.front();
    Q.pop();

    int b = 0, r = 0;
    vi undefined;
    each(j, cv[i]) {
      if (ans[j] == 'B') b++;
      if (ans[j] == 'R') r++;
      if (ans[j] == ' ') undefined.push_back(j);
    }
    if (b) {
      each(j, undefined) ans[j] = 'R';
    }
    if (r) {
      each(j, undefined) ans[j] = 'B';
    }
    if (b == 0 and r == 0) {
      rep(k, sz(undefined)) {
        int j = undefined[k];
        ans[j] = k % 2 ? 'B' : 'R';
      }
    }

    rep(j, sz(cv[i])) {
      int u = cv[i][j];
      int v = cv[i][(j + 1) % sz(cv[i])];
      each(ii, related[minmax(u, v)]) add(ii);
    }
  }

  out(ans);
}

void Nyaan::solve() {
  int t = 1;
  in(t);
  while (t--) q();
}