#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<int(n); i++)
const i64 INF = 1001001001001001001;
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
using namespace std;

void testcase(){
    int H, W; cin >> H >> W;
    vector<string> A(H); rep(y,H) cin >> A[y];
    rep(t,2){
        bool ok = true; {
            vector<int> Q(H+W);
            rep(y,H) rep(x,W) if(A[y][x] == 'W') Q[y+x] ^= 1;
            if(Q != vector<int>(H+W,0)) ok = false;
        }
        if(!ok){
            rep(y,H) rep(x,W) A[y][x] ^= 'B' ^ 'W';
            continue;
        }
        rep(y,H) rep(x,W) A[y][x] = (A[y][x] == 'W' ? 1 : 0);
        vector<string> ans;
        for(int t=-(H-1); t<W-2; t++){
            string f;
            int y = 0, x = 0;
            A[y][x] ^= 1;
            rep(i,H+W-2){
                if(x==W-1){ f.push_back('D'); y++; }
                else if(y==H-1){ f.push_back('R'); x++; }
                else if(x-y > t+1){ f.push_back('D'); y++; }
                else if(x-y <= t){ f.push_back('R'); x++; }
                else{
                    if(A[y+1][x]){ f.push_back('D'); y++; }
                    else { f.push_back('R'); x++; }
                }
                A[y][x] ^= 1;
            }
            ans.push_back(f);
        }
        if(A[0][W-1]) ans.push_back(string(W-1,'R') + string(H-1,'D'));
        cout << "YES" << endl;
        cout << ans.size() << endl;
        for(auto& a : ans) cout << a << endl;
        return;
    }
    cout << "NO" << endl;
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int T; cin >> T;
    rep(t,T) testcase();
    return 0;
}