#line 1 "L.cpp"
// #pragma GCC target("avx2,avx512f,avx512vl,avx512bw,avx512dq,avx512cd,avx512vbmi,avx512vbmi2,avx512vpopcntdq,avx512bitalg,bmi,bmi2,lzcnt,popcnt")
// #pragma GCC optimize("Ofast")

#line 2 "/home/sigma/comp/library/template.hpp"

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb push_back
#define eb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> bool chmax(T& x, U y){
	if(x<y){ x=y; return true; }
	return false;
}
template<class T,class U> bool chmin(T& x, U y){
	if(y<x){ x=y; return true; }
	return false;
}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class T> int lwb(const V<T>& v, const T& a){return lower_bound(all(v),a) - v.begin();}
template<class T>
V<T> Vec(size_t a) {
    return V<T>(a);
}
template<class T, class... Ts>
auto Vec(size_t a, Ts... ts) {
  return V<decltype(Vec<T>(ts...))>(a, Vec<T>(ts...));
}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

template<class D> D divFloor(D a, D b){
	return a / b - (((a ^ b) < 0 && a % b != 0) ? 1 : 0);
}
template<class D> D divCeil(D a, D b) {
	return a / b + (((a ^ b) > 0 && a % b != 0) ? 1 : 0);
}
#line 5 "L.cpp"

void solve(){
	int H,W; cin >> H >> W;
	VV<int> A_(H,V<int>(W));
	rep(i,H){
		string t; cin >> t;
		rep(j,W) if(t[j] == 'B') A_[i][j] = 1;
	}
	rep(_,2){
		auto A = A_;
		if(_){
			rep(i,H) rep(j,W) A[i][j] ^= 1;
		}
		V<string> ans;
		rep(t,H+W-1){
			show("-----------");
			show(t);
			string s;
			int x = 0, y = 0;
			show(A);
			A[0][0] ^= 1;
			rep(h,H-1){
				// t = h-w + (W-1)
				int w = h-t+(W-1);
				shows(h,w);
				shows(x,y);
				if(w<0 || w>=W || A[h][w] == 0){
					s += 'D'; x++; A[x][y] ^= 1;
					continue;
				}
				assert(y <= w);
				while(y != w){
					s += 'R'; y++; A[x][y] ^= 1;
				}
				s += 'D'; x++; A[x][y] ^= 1;
			}
			assert(x == H-1);
			while(y != W-1){
				s += 'R'; y++; A[x][y] ^= 1;
			}
			ans.pb(s);
		}
		show(A);
		if(A[0][0]){
			A[0][0] ^= 1;
			int x = 0, y = 0;
			string s;
			rep(h,H-1){
				s += 'D'; x++; A[x][y] ^= 1;
			}
			rep(w,W-1){
				s += 'R'; y++; A[x][y] ^= 1;
			}
			ans.pb(s);
		}
		bool ok = true;
		rep(i,H) rep(j,W) if(A[i][j]) ok = false;
		if(ok){
			cout << "YES\n";
			cout << ans.size() << endl;
			for(auto s: ans) cout << s << endl;
			return;
		}
	}
	cout << "NO\n";
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	int T; cin >> T;
	while(T--) solve();
}