#include <bits/stdc++.h>

#define int int64_t

const int kMaxN = 105, kInf = 1e18, kD[][2] = {{0, 1}, {0, -1}, {1, 0}, {1, -1}};

int n, m;
std::string s[105];

int getid(int x, int y, int o = 0) { return (x - 1) * m + y + o * n * m; }

namespace Dinic {
const int kMaxN = 3e4 + 5, kMaxM = 1e6 + 5;
struct Edge {
  int v, w, pre;
} e[kMaxM];

int tot = 1, n, s, t, tail[kMaxN], cur[kMaxN], dep[kMaxN];
bool vis[kMaxN];

void set(int _n, int _s, int _t) { n = _n, s = _s, t = _t; }
void adde(int u, int v, int w) { e[++tot] = {v, w, tail[u]}, tail[u] = tot; }
void add(int u, int v, int w) { adde(u, v, w), adde(v, u, 0); }
void init() {
  for (int i = 0; i <= tot; ++i) e[i] = {0, 0, 0};
  for (int i = 0; i <= n; ++i) tail[i] = cur[i] = dep[i] = 0;
  n = s = t = 0, tot = 1;
}

bool bfs() {
  std::queue<int> q;
  for (int i = 1; i <= n; ++i)
    cur[i] = tail[i], dep[i] = kInf, vis[i] = 0;
  q.emplace(s), dep[s] = 0, vis[s] = 1;
  while (!q.empty()) {
    int u = q.front(); q.pop();
    for (int i = tail[u]; i; i = e[i].pre) {
      int v = e[i].v, w = e[i].w;
      if (w && !vis[v]) {
        dep[v] = dep[u] + 1, vis[v] = 1, q.emplace(v);
      }
    }
  }
  return vis[t];
}

int dfs(int u, int lim) {
  if (u == t || !lim) return lim;
  int flow = 0;
  for (int &i = cur[u]; i; i = e[i].pre) {
    int v = e[i].v, w = e[i].w;
    if (w && dep[v] == dep[u] + 1) {
      int fl = dfs(v, std::min(lim, w));
      if (!fl) dep[v] = kInf;
      lim -= fl, flow += fl;
      e[i].w -= fl, e[i ^ 1].w += fl;
      if (!lim) break;
    }
  }
  return flow;
}

int maxflow() {
  int ans = 0;
  for (; bfs(); ans += dfs(s, kInf)) {}
  return ans;
}
} // namespace Dinic

void dickdreamer() {
  Dinic::init();
  std::cin >> n >> m;
  int ss = 3 * n * m + 1, tt = ss + 1, tot = 0;
  Dinic::set(tt, ss, tt);

  // 与 ss 相连：W，与 tt 相连 ： B
  for (int i = 1; i <= n; ++i) {
    std::cin >> s[i];
    s[i] = " " + s[i];
    for (int j = 1; j <= m; ++j) {
      if (((i + j) & 1) && s[i][j] != '?')
        s[i][j] = 'B' + 'W' - s[i][j];
      if (s[i][j] == '?') ++tot;
      if (s[i][j] == '?' || s[i][j] == 'W') Dinic::add(ss, getid(i, j), 1);
      else Dinic::add(ss, getid(i, j), kInf);
      if (s[i][j] == '?' || s[i][j] == 'B') Dinic::add(getid(i, j), tt, 1);
      else Dinic::add(getid(i, j), tt, kInf);
    }
  }
  for (int i = 1; i < n; ++i) {
    for (int j = 1; j < n; ++j) {
      int t1 = getid(i, j, 1), t2 = getid(i, j, 2);
      Dinic::add(ss, t1, 1e9), Dinic::add(t2, tt, 1e9);
      Dinic::add(t1, getid(i, j), kInf), Dinic::add(t1, getid(i, j + 1), kInf),
      Dinic::add(t1, getid(i + 1, j), kInf), Dinic::add(t1, getid(i + 1, j + 1), kInf);
      Dinic::add(getid(i, j), t2, kInf), Dinic::add(getid(i, j + 1), t2, kInf);
      Dinic::add(getid(i + 1, j), t2, kInf), Dinic::add(getid(i + 1, j + 1), t2, kInf);
    }
  }
  int cnt = Dinic::maxflow() - n * m;
  assert(cnt % 1000000000 == 0);
  // std::cerr << cnt << '\n';
  std::cout << 2 * (n - 1) * (m - 1) - cnt / 1000000000 << '\n';
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      if (Dinic::vis[getid(i, j)]) s[i][j] = 'B';
      else s[i][j] = 'W';
      if ((i + j) & 1) s[i][j] = 'B' + 'W' - s[i][j];
      std::cout << s[i][j];
    }
    std::cout << '\n';
  }
}

int32_t main() {
#ifdef ORZXKR
  freopen("in.txt", "r", stdin);
  freopen("out.txt", "w", stdout);
#endif
  std::ios::sync_with_stdio(0), std::cin.tie(0), std::cout.tie(0);
  int T = 1;
  std::cin >> T;
  while (T--) dickdreamer();
  // std::cerr << 1.0 * clock() / CLOCKS_PER_SEC << "s\n";
  return 0;
}