#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define int ll
#define ff first
#define ss second
#define pb push_back
#define eb emplace_back
typedef pair<int, int> pii;
const int inf=INT_MAX;
const int maxn=1e6+10;

int n, m;
vector<int> g[maxn];
int deg[maxn];

int l[maxn];
int r[maxn];

int cor[maxn];

int32_t main()
{
    ios::sync_with_stdio(0);cin.tie(0);

    int T; cin>> T;
    while(T--)
    {
        cin>> n>> m;
        int sdg = 0;
        for(int i=1; i<=n; i++)
        {
            g[i].clear();
            cor[i] = deg[i] = l[i] = r[i] = 0;
        }
        set<int> all;
        set<pii> alldg;
        for(int i=0; i<m; i++)
        {
            int u, v; cin>> u>> v;
            u++, v++;
            g[u].pb(v);
            g[v].pb(u);
            deg[u]++;
            deg[v]++;
            sdg += 2;
        }
        for(int i=1; i<=n; i++)
        {
            all.insert(i);
            alldg.emplace(deg[i], i);
        }
        deque<int> ordem;
        while(sdg)
        {
            auto it1 = alldg.begin();
            int v = (*it1).ss;
            // alldg.erase(it1);
            // all.erase(v);
            assert(deg[v] == 0);
            // u primeiro maior que v, w primeiro menor que v, indices mod n
            vector<int> caras;
            auto it = all.find(v);
            while(!deg[*it])
            {
                caras.pb(*it);
                if(it == all.begin()) it = all.end();
                it--;
            }
            int u = *it;
            it = all.find(v);
            it++; if(it == all.end()) it = all.begin();
            while(!deg[*it])
            {
                caras.pb(*it);
                it++; if(it == all.end()) it = all.begin();
            }
            int w = *it;
            for(int x: caras)
            {
                ordem.pb(x);
                l[x] = u;
                all.erase(x);
                alldg.erase(pii(deg[x], x));
            }
            assert(u != v);
            alldg.erase(pii(deg[w], w));
            deg[w]--;
            alldg.insert(pii(deg[w], w));
            alldg.erase(pii(deg[u], u));
            deg[u]--;
            alldg.insert(pii(deg[u], u));
            sdg -= 2;
        }
        int curcor = 1;
        for(int x: all)
        {
            cor[x] = curcor;
            curcor = 3 - curcor;
        }
        reverse(ordem.begin(), ordem.end());
        for(int v: ordem)
        {
            assert(l[v]);
            cor[v] = 3 - cor[l[v]];
        }
        for(int i=1; i<=n; i++)
        {
            if(cor[i] == 1) cout<< 'B';
            else cout<< 'R';
        }
        cout<< "\n";
    }

    return 0;
}