//#pragma GCC optimize(3,"Ofast","inline")
#include <bits/stdc++.h>
using namespace std;  

#define int long long
#define pii pair<int,int>
#define mkp make_pair
#define fi first
#define se second
#define pb push_back
#define lowbit(x) ((x)&(-x))

#define ppc __builtin_popcount

#define lc(p) ((p)<<1)
#define rc(p) ((p)<<1|1)

#define sqr(x) ((x)*(x))

// #define mod 1000000007
// #define mod 998244353
#define eps 1e-10

#define debug cout<<__LINE__<<" "<<__FUNCTION__<<"\n";
#define spa putchar(' ')
#define ero putchar('\n')

mt19937 rnd(time(0));

constexpr int N=1e6+10,inf=1e18;

inline int read(){
	int x=0,f=1;char ch=getchar();
	while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
	while (ch>='0'&&ch<='9'){x=x*10+ch-48;ch=getchar();}
	return x*f;
}
inline void write(int x){
	if(!x)putchar('0');
	if(x<0)x=-x,putchar('-');
	int cnt=0,a[30];
	while(x)a[++cnt]=x%10,x/=10;
	while(cnt--)putchar(a[cnt+1]+'0');
}

int nxt[N],a[N];

void solve(){
    int n=read(),m=read();
    if(!m){
        putchar('B');
        for(int i=2;i<=n;i++){
            putchar('R');
        }
        ero;
        return ;
    }
    memset(a,0,sizeof(a));
    for(int i=1;i<=n;i++){
        nxt[i]=i-1;
    }
    for(int i=1;i<=m;i++){
        int u=read()+1,v=read()+1;
        if(u>v){
            swap(u,v);
        }
        nxt[v]=min(nxt[v],u);
    }
    // for(int i=1;i<=n;i++){
    //     cout<<f[i]<<" ";
    // }
    // cout<<"\n";
    for(int i=1;i<=n;i++){
        a[i]=a[nxt[i]]^1;
    }
    for(int i=1;i<=n;i++){
        // write(f[i]),spa;
        if(a[i]){
            putchar('R');
        }
        else{
            putchar('B');
        }
    }
    ero;
}

signed main(){
	// freopen(".in","r",stdin);
	// freopen(".out","w",stdout);
	// ios::sync_with_stdio(0),cin.tie(0),cout.tie(0); 
    int T=read();
    // int T=1;
    while(T--){
        solve();
    }
	return 0;
}