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

const int MAXN = 1e6 + 5;
int n, m;

int tot, h[MAXN];
struct edge {
	int to, nxt;
} e[MAXN << 1];

void add (int x, int y) {
	e[++tot] = (edge) { y, h[x] };
	h[x] = tot;
}

int col[MAXN];
void dfs (int x, int typ = 1) {
	col[x] = typ;
	for (int u = h[x]; u; u = e[u].nxt)
		if (!col[e[u].to]) dfs (e[u].to, typ % 2 + 1);
}

int T;
int main() {
	int i,j,k;
	int x, y;
	cin >> T;
	while (T--) {
		cin >> n >> m;
		tot = 0;
		for (i = 1; i <= n; ++i) h[i] = 0, col[i] = 0;
		for (i = 1; i <= m; ++i)
			cin >> x >> y, ++x, ++y, add (x, y), add (y, x);
		dfs (1);
		for (i = 2; i <= n; ++i) {
			if (col[i]) continue ;
			col[i] = col[i - 1] % 2 + 1;
		}
		for (i = 1; i <= n; ++i)
			putchar (col[i] == 1 ? 'R' : 'B');
		puts ("");
	}
	return 0;
}