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

int main() {
    int T;
    cin >> T;
    while (T--) {
        int n, m;
        cin >> n >> m;
        vector<string> grid(n);
        for (int i = 0; i < n; ++i) cin >> grid[i];

        bool all_white = true, all_black = true;
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                if (grid[i][j] == 'W') all_black = false;
                else all_white = false;
            }
        }
        if (all_white || all_black) {
            cout << "YES\n0\n";
            continue;
        }

        if (n == 1 || m == 1) {
            int total = n * m;
            int black = 0;
            for (int i = 0; i < n; ++i)
                for (int j = 0; j < m; ++j)
                    black += (grid[i][j] == 'B');
            bool possible = false;
            if (total % 2 == 0) {
                if (black == 0 || black == total) possible = true;
                else if (total - black == 0 || total - black == total) possible = true;
            } else {
                if (black == 0 || black == total) possible = true;
                else if (total - black == 0 || total - black == total) possible = true;
            }
            if (!possible) {
                cout << "NO\n";
                continue;
            }
            cout << "YES\n1\n";
            if (n == 1) cout << string(m-1, 'R') << '\n';
            else cout << string(n-1, 'D') << '\n';
            continue;
        }

        bool found = false;
        for (int target = 0; target < 2; ++target) { // 0: B, 1: W
            vector<int> diag_cnt(n + m, 0);
            for (int i = 0; i < n; ++i) {
                for (int j = 0; j < m; ++j) {
                    bool is_error = (target == 0) ? (grid[i][j] == 'W') : (grid[i][j] == 'B');
                    int k = i + j;
                    if (is_error) diag_cnt[k]++;
                }
            }
            bool valid = true;
            for (int k = 0; k < n + m - 1; ++k) {
                if (diag_cnt[k] % 2 != 0) {
                    valid = false;
                    break;
                }
            }
            if (valid) {
                found = true;
                break;
            }
        }

        if (found) {
            string path1 = string(m-1, 'R') + string(n-1, 'D');
            string path2 = string(n-1, 'D') + string(m-1, 'R');
            cout << "YES\n2\n" << path1 << '\n' << path2 << '\n';
        } else {
            cout << "NO\n";
        }
    }
    return 0;
}