#include<bits/stdc++.h>

#define ll long long
#define pi pair<int,int>
#define vi vector<int>
#define cpy(x,y,s) memcpy(x,y,sizeof(x[0])*(s))
#define mset(x,v,s) memset(x,v,sizeof(x[0])*(s))
#define all(x) begin(x),end(x)
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ary array
#define eb emplace_back
#define IL inline
#define For(i,j,k) for(int i=(j);i<=(k);i++)
#define Fol(i,k,j) for(int i=(k);i>=(j);i--)

using namespace std;

#define N 205

int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0' || ch>'9')f=(ch=='-'?-1:f),ch=getchar();
    while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    return x*f;
}
void write(int x){
    if(x<0)x=-x,putchar('-');
    if(x/10)write(x/10);
    putchar(x%10+'0');
}

void debug(auto &&...x){
    ((cerr<<x<<' '),...);
    cerr<<'\n';
}

char s[N][N];
int a[N][N];
int n,m;

bool check(char t){
    For(i,1,n)For(j,1,m)a[i][j]=(s[i][j]==t);
    vector<string> res;
    For(_,1,401){
        string now="";int pos=1,flag=0;
        For(i,1,n)For(j,1,m)if(a[i][j]==1)flag=1;
        if(!flag)break;
        if(_==401)return false;
        For(i,1,n){
            int step=pos;a[i][pos]^=1;
            Fol(j,m,pos+1)if(a[i][j]){step=j;break;}
            while(pos<step){pos++;a[i][pos]^=1;now+='R';}
            if(i!=n)now+='D';
        }
        while(pos+1<=m){pos++;now+='R';}
        res.pb(now);
    }
    cout<<"YES"<<endl;
    cout<<res.size()<<endl;
    for(auto v:res)cout<<v<<endl;
    return true;
}

void solve(){
    n=read(),m=read();
    For(i,1,n)scanf("%s",s[i]+1);
    if(check('W'))return;
    if(check('B'))return;printf("NO\n");
}

int main(){
    #ifdef EAST_CLOUD
    freopen("a.in","r",stdin);
    //freopen("a.out","w",stdout);
    #endif

    int T=read();while(T--)solve();
 
}