#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
const int N = 3e5 + 5;
const int mod = 1e9 + 5;
int n, m;

vector<pair<ll, ll>> e;
vector<ll> v[200005];
ll co[200005];
bool vis[1000005];
void dfs(ll x, ll color, ll fa) {
    vis[x] = 1;
    if (co[x] == -1 && v[x].size() >=1) {
        co[x] = 1;
    }
    for (auto i : v[x]) {
        if (vis[i]) {
            continue;
        }
        if (i == fa)continue;
        if (co[i] == -1)
        {
            co[i] = co[x] ^ 1;
        }
        dfs(i, co[i], x);
    }
}
void solve()
{
    cin >> n >> m;
    e.clear();
    for (int i = 0;i < n;i++) {
        v[i].clear();
        co[i] = -1;
        vis[i] = 0;
    }
    for (int i = 1;i <= m;i++) {
        ll x, y;cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
        e.push_back(make_pair(x, y));
    }
    for (int i = 0;i < n;i++) {
        // if (co[i] == -1) co[i] = 1;
        dfs(i, 1, -1);
    }
    bool flag = 0;
    for (int i = 0;i < e.size();i++) {
        if (co[e[i].first] == co[e[i].second]) {
            // cout << e[i].first << " " << e[i].second << endl;
            for (int j = e[i].first + 1;j != e[i].second;j++) {
                if (j >= n)j %= n;
                // cout << j << endl;
                // if (co[j] == co[e[i].first] ^ 1)break;
                if (co[j] == -1) {
                    co[j] = co[e[i].first] ^ 1;
                    break;
                }
            }
            for (int j = e[i].second + 1;j != e[i].first;j++) {
                if (j >= n)j %= n;
                // if (co[j] == co[e[i].first] ^ 1)break;
                if (co[j] == -1) {
                    co[j] = co[e[i].first] ^ 1;
                    break;;
                }
            }
            break;
        }
    }
    // for (int i = 0;i < n;i++)cout << co[i] <<" ";
    for (int i = 0;i < n;i++) {
        if (co[i] == -1) {
            if (flag == 0) {
                cout << "R";
                flag = 1;
            }
            else {
                cout << "B";
            }
        }
        else if (co[i] == 1) {
            cout << "R";
        }
        else {
            cout << "B";
        }
    }
    cout << "\n";
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}