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

using ll = long long;
using ull = unsigned long long;

string to_string(const string &s) {
  return '"' + s + '"';
}

string to_string(bool b) {
  return b ? "true" : "false";
}

template <typename A, typename B>
string to_string(const pair<A, B> &p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename T>
string to_string(const T &v) {
  string s = "{";
  bool first = true;
  for (const auto &it : v) {
    if (!first)
      s += ", ";
    else
      first = false;
    s += to_string(it);
  }
  return s += "}";
}

void debug_out() {
  cerr << endl;
}

template <typename T, typename... Args>
void debug_out(const T &first, const Args&... rest) {
  cerr << to_string(first) << " ";
  debug_out(rest...);
}

#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

auto startTime = high_resolution_clock::now();
int get_time() {
  auto stopTime = chrono::high_resolution_clock::now();
  auto duration = duration_cast<milliseconds>(stopTime - startTime);
  return duration.count(); // in ms
}

int n, m;

bool solve(vector<vector<int>> v) {
  if (v[1][1] != v[n][m]) {
    return 0;
  }

  auto v2 = v;
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      v2[i][j] = 0;
    }
  }

  if (v[1][1] == 1) {
    v2[1][1] = 1;
  }

  for (int d = 1; d <= n + m - 1; ++d) {
    for (int i = 1; i <= n; ++i) {
      int j = d - i + 1;

      if (j < 1 || j > n) {
        continue;
      }

      if (v[i][j] % 2 != v2[i][j] % 2) {
        return 0;
      }

      if (v[i][j] > 400) {
        return 0;
      }

      if (j + 1 <= m) {
        if (i + 1 <= n) {
          if (v[i][j + 1] % 2 != v2[i][j + 1] % 2) {
            if (v2[i][j] == 0) {
              v2[i][j] += 2;
            }
            v2[i][j + 1] += 1;
            v2[i + 1][j] += v2[i][j] - 1;
          } else {
            v2[i + 1][j] += v2[i][j];
          }
        } else {
          v2[i][j + 1] += v2[i][j];
        }
      } else if (i + 1 <= n) {
        v2[i + 1][j] += v2[i][j];
      }
    }
  }

  cout << "YES\n";
 // for (int i = 1; i <= n; ++i) {
 //   for (int j = 1; j <= m; ++j) {
 //     cout << v2[i][j] << " ";
 //   }
 //   cout << "\n";
 // }
  cout << v2[n][m] << "\n";

  while (v2[n][m] > 0) {
    int i = n, j = m;
    string s;

    while (i > 1 || j > 1) {
      --v2[i][j];
      if (i - 1 >= 1 && v2[i - 1][j] > 0) {
        s.push_back('D');
        --i;
      } else if (j - 1 >= 1 && v2[i][j - 1] > 0) {
        s.push_back('R');
        --j;
      } else if (i - 1 >= 1) {
        v2[i - 1][j] += 2;
        s.push_back('D');
        --i;
      } else {
        v2[i][j - 1] += 2;
        s.push_back('R');
        --j;
      }
    }
    --v2[1][1];

    reverse(s.begin(), s.end());
    cout << s << "\n";
  }

  return 1;
}

void solve() {
  cin >> n >> m;

  vector<vector<int>> v(n + 1, vector<int>(m + 1));

  for (int i = 1; i <= n; ++i) {
    string s;
    cin >> s;

    for (int j = 1; j <= m; ++j) {
      v[i][j] = (s[j - 1] == 'W') ? 0 : 1;
    }
  }

  bool ok = solve(v);
  if (ok) {
    return;
  }

  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      v[i][j] ^= 1;
    }
  }

  ok = solve(v);
  if (!ok) {
    cout << "NO\n";
  }
}

int main() {
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);

  int t = 1;
  cin >> t;
  while (t--)
    solve();

  return 0;
}