// l.cpp
#include <bits/stdc++.h>
using namespace std;
int n, m;
char s[205][205];
int cnt[405][2], to;
void solve() {
    cin >> n >> m;
    memset(cnt, 0, n + m << 3);
    for (int i = 0; i < n; i++) {
    	cin >> s[i];
    	for (int j = 0; j < m; j++) {
    		cnt[i + j][s[i][j] == 'W'] += 1;
    	}
    }
    to = 3;
    for (int i = 1; i < n + m - 1; i++) {
    	if (cnt[i][0] + cnt[0][0] & 1) {
    		to &= 2;
    	}
    	if (cnt[i][1] + cnt[0][1] & 1) {
    		to &= 1;
    	}
    }
    if (to == 0) {
    	printf("NO\n");
    	return;
    }
    if (to == 3) {
    	printf("YES\n0\n");
    	return;
    }
    to = __lg(to);
    vector<string> ans;
    for (int u = 0; u < n + m - 1; u++) {
    	vector<pair<int, int> > q;
    	for (int i = max(0, u - m + 1); i <= u && i < n; i++) {
    		int j = i - u + m - 1;
    		if ((i == n - 1) + (j == 0) != 1 && (s[i][j] == 'W') == to) {
    			q.push_back({i, j});
    		}
    	}
    	if (q.empty()) {
    		continue;
    	}
    	q.push_back({n - 1, m - 1});
    	string S;
    	int x = 0, y = 0;
    	s[x][y] ^= 'B' ^ 'W';
    	for (auto [i, j] : q) {
    		while (x < i) {
    			x += 1;
    			S += 'D';
    			s[x][y] ^= 'B' ^ 'W';
    		}
    		while (y < j) {
    			y += 1;
    			S += 'R';
    			s[x][y] ^= 'B' ^ 'W';
    		}
    	}
    	ans.push_back(S);
    }
    cout << "YES\n" << ans.size() << "\n";
    for (string &s : ans)
    	cout << s << "\n";
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int T;
    cin >> T;
    while (T--) solve();
    return 0;
}