#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 205;

int T, n, m, f[N << 1], g[N << 1];

string s[N];

vector <pair <int, int> > vec[N << 1];

inline void op(int i, int j) {
	s[i][j] = (s[i][j] == 'W') ? 'B' : 'W';
}

inline void solve() {
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		cin >> s[i];
		s[i] = "#" + s[i];
	}
	for (int i = 0; i <= n + m; ++i) {
		vec[i].clear();
		f[i] = 0;
		g[i] = 0;
	}
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= m; ++j) {
			if (s[i][j] == 'W') {
				f[i + j] ^= 1;
			} else {
				g[i + j] ^= 1;
			}
		}
	}
	bool flg1 = 1, flg2 = 1;
	for (int i = 3; i <= n + m; ++i) {
		if (f[i] != f[i - 1]) {
			flg1 = 0;
		}
		if (g[i] != g[i - 1]) {
			flg2 = 0;
		}
	}
	if (!flg1 && !flg2) {
		cout << "NO\n";
		return;
	}
	cout << "YES\n";
	char col = flg1 ? 'B' : 'W';
	bool flg = (s[1][1] != col);
	if (flg) {
		for (int i = 1; i <= n; ++i) {
			op(i, 1);
		}
		for (int i = 2; i <= m; ++i) {
			op(n, i);
		}
	}
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= m; ++j) {
			if (s[i][j] != col) {
				vec[j - i + n].emplace_back(make_pair(i + 1, j));
				op(i, j), op(i + 1, j - 1);
			}
		}
	}
	int cnt = 0;
	for (int i = 0; i <= n + m; ++i) {
		if (!vec[i].size()) {
			continue;
		}
		++cnt;
	}
	if (flg) {
		cout << (cnt << 1 | 1) << "\n";
		for (int i = 1; i < n; ++i) {
			cout << "D";
		}
		for (int i = 2; i <= m; ++i) {
			cout << "R";
		}
		cout << "\n";
	} else {
		cout << (cnt << 1) << "\n";
	}
	for (int i = 0; i <= n + m; ++i) {
		if (!vec[i].size()) {
			continue;
		}
		int x = 1, y = 1;
		for (auto u: vec[i]) {
			while (x < u.first - 1) {
				cout << "D";
				++x;
			}
			while (y < u.second - 1) {
				cout << "R";
				++y;
			}
			cout << "DR";
			x = u.first, y = u.second;
		}
		while (x < n) {
			cout << "D";
			++x;
		}
		while (y < m) {
			cout << "R";
			++y;
		}
		cout << "\n";
		x = 1, y = 1;
		for (auto u: vec[i]) {
			while (x < u.first - 1) {
				cout << "D";
				++x;
			}
			while (y < u.second - 1) {
				cout << "R";
				++y;
			}
			cout << "RD";
			x = u.first, y = u.second;
		}
		while (x < n) {
			cout << "D";
			++x;
		}
		while (y < m) {
			cout << "R";
			++y;
		}
		cout << "\n";
	}
}

int main() {
	#ifdef LOCAL
		assert(freopen("test.in", "r", stdin));
		assert(freopen("test.out", "w", stdout));
	#endif
	ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
	cin >> T;
	while (T--) {
		solve();
	}
	return 0;
}