#include<iostream>
#include<cstdio>
#include<unordered_map>
#include<cmath>
#include<vector>
#include<queue>
#include<map>
#include<stack>
#include<array>
#include<set>
#include<algorithm>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
constexpr ll mod = 1e9 + 7;
void speed()
{
 ios::sync_with_stdio(0);
 cin.tie(0);
 cout.tie(0);
}
ll ksm(ll num, ll cnt)
{
 ll temp = 1;
 ll mul = num;
 while (cnt)
 {
  if (cnt & 1) temp = (temp * mul) % mod;
  mul = (mul * mul) % mod;
  cnt >>= 1;
 }
 return temp;
}
vector<int>edge[200005];
void solve()
{
 int n, m;
 cin >> n >> m;
 for (int i = 1; i <= m; i++)
 {
  int u, v;
  cin >> u >> v;
  edge[u].push_back(v);
  edge[v].push_back(u);
 }
 vector<int>is(n + 1);
 queue<int>q;
 for (int i = 1; i <= n; i++)
 {
  if (is[i] == 0)
  {
   q.push(i);
   if (i == 1)
    is[i] = 1;
   else
    is[i] = -is[i - 1];
   while (!q.empty())
   {
    int f = q.front();
    q.pop();
    if (i != f)
    {
     if (is[f] != 0) continue;
    }
    for (auto j : edge[f])
    {
     if (!is[j])
     {
      is[j] = -is[f];
      q.push(j);
     }
    }
   }
  }
 }
 for (int i = 1; i <= n; i++)
 {
  if (is[i] == 1)
   cout << "R";
  else
   cout << "B";
 }
 cout << endl;
 for (int i = 1; i <= n; i++)
  edge[i].clear();
}
int main()
{
 speed();
 int t;
 cin >> t;
 //t = 1;
 while (t--)
 {
  solve();
 }
 return 0;
}