#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], tmp[N];
vector <string> ans;

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

inline void op(string S) {
	int x = 1, y = 1;
	op(1, 1);
	for (auto ch: S) {
		if (ch == 'D') {
			++x;
		} else {
			++y;
		}
		op(x, y);
	}
}

inline void solve() {
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		cin >> s[i];
		s[i] = "#" + s[i];
	}
	bool flg = 0;
	if (n > m) {
		flg = 1;
		for (int i = 1; i <= n; ++i) {
			tmp[i] = s[i];
		}
		swap(n, m);
		for (int i = 1; i <= n; ++i) {
			s[i] = "#";
			for (int j = 1; j <= m; ++j) {
				s[i] += tmp[j][i];
			}
		}
	}
	for (int i = 0; i <= n + m; ++i) {
		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';
	ans.clear();
	for (int k = 1 - m; k < 0; ++k) {
		int x = 1, y = 1;
		string S = "";
		for (int i = 1; i <= n; ++i) {
			for (int j = 1; j <= m; ++j) {
				if (i - j != k) {
					continue;
				}
				if (i == n) {
					continue;
				}
				while (y < j - 1) {
					S += "R";
					++y;
				}
				if (s[i][j] == col) {
					S += "DR";
				} else {
					S += "RD";
				}
				++x, ++y;
			}
		}
		while (x < n) {
			S += "D";
			++x;
		}
		while (y < m) {
			S += "R";
			++y;
		}
		op(S);
		ans.emplace_back(S);
	}
	for (int k = n - 1; k > 1; --k) {
		int x = 1, y = 1;
		string S = "";
		for (int i = 1; i <= n; ++i) {
			for (int j = 1; j <= m; ++j) {
				if (i - j != k) {
					continue;
				}
				while (x < i - 1) {
					S += "D";
					++x;
				}
				if (s[i][j] == col) {
					S += "RD";
				} else {
					S += "DR";
				}
				++x, ++y;
			}
		}
		while (x < n) {
			S += "D";
			++x;
		}
		while (y < m) {
			S += "R";
			++y;
		}
		op(S);
		ans.emplace_back(S);
	}
	if (s[1][1] != col) {
		string S = "";
		int x = 1, y = 1;
		while (x < n || y < m) {
			if (x < n && s[x + 1][y] != col) {
				++x, S += "D";
			} else {
				++y, S += "R";
			}
		}
		op(S);
		ans.emplace_back(S);
	}
	cout << ans.size() << "\n";
	for (auto u: ans) {
		if (flg) {
			for (auto &v: u) {
				v = (v == 'R' ? 'D' : 'R');
			}
		}
		cout << u << "\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;
}