#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);
}
int cnt = 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;
	cnt++;
	cin >> n >> m;
	if (cnt == 22)
	{
		cout << "N:" << n << " M:" << m << endl;
	}
	for (int i = 1; i <= m; i++)
	{
		int u, v;
		cin >> u >> v;
		if (cnt == 22)
		{
			cout << u << " " << v << endl;
		}
		edge[u+1].push_back(v+1);
		edge[v+1].push_back(u+1);
	}
	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;
}