#include <bits/stdc++.h>
using namespace std;
char c[205][205];
int a[205][205];
int n, m;
string ans[405];

bool ck(char c2) {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			a[i][j] = (c[i][j] == c2);
		}
	}
	int cnt;
	for (cnt = 1; cnt <= 401; cnt++) {
		bool ok = 1;
		for (int i = 1; i <= n; i++)
			for (int j = 1; j <= m; j++)
				if (a[i][j])
					ok = 0;
		if (ok) {
			cnt--;
			break;
		}
		if (cnt == 401)
			return 0;
		ans[cnt] = "";
		int y = 1;
		for (int i = 1; i <= n; i++) {
			a[i][y] ^= 1;
			int k = 1;
			for (int j = m; j; j--) {
				if (a[i][j]) {
					k = j;
					break;
				}
			}
			while (y < k) {
				a[i][++y] ^= 1;
				ans[cnt] += 'R';
			}
			if (i < n)
				ans [cnt] += 'D';
			else
				while (y < m) {
					a[n][++y] ^= 1;
					ans[cnt].push_back('R');
				}
		}
	}
	puts("YES");
	cout << cnt << '\n';
	for (int ii = 1; ii <= cnt; ii++)
		cout << ans[ii] << '\n';;
	return 1;
}

void solve() {
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++)
			cin >> c[i][j];
	if (!ck('B') && !ck('W'))
		puts("NO");
	return ;
}

signed main() {
	int T;
	cin >> T;
	while (T--) {
		solve();
	}
}