#include <algorithm>
#include <cstdio>
#include <queue>
#include <vector>

#define debug(...) fprintf(stderr, __VA_ARGS__)

const int N = 105;
const int Inf = 1e9;

int vis[N * N * 2], pd[N * N * 2];

namespace Dinic {
const int N = 100 * 100 * 2 + 5;
const int M = N * 100;

int tot, head[N], cur[N];
struct Edge {
  int nxt, v, w;
} e[M];
inline void addEdge(int u, int v, int w) {
  e[++tot] = {head[u], v, w};
  head[u] = tot;
}
inline void add(int u, int v, int w) {
  addEdge(u, v, w);
  addEdge(v, u, 0);
}

int n;
int dep[N];
bool bfs(int s, int t) {
  for (int i = 0; i <= n; ++i) dep[i] = 0;
  dep[s] = 1;
  std::queue<int> q;
  q.push(s);
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    for (int i = head[u]; i; i = e[i].nxt) {
      int v = e[i].v, w = e[i].w;
      if (w && !dep[v]) {
        dep[v] = dep[u] + 1;
        q.push(v);
      }
    }
  }
  return dep[t];
}
int dfs(int u, int t, int in) {
  if (u == t) return in;
  int out = 0;
  for (int &i = cur[u]; i; i = e[i].nxt) {
    int v = e[i].v, w = e[i].w;
    if (w && dep[v] == dep[u] + 1) {
      int res = dfs(v, t, std::min(in, w));
      out += res;
      e[i].w -= res, e[i ^ 1].w += res;
      if (in == out) return in; 
    }
  }
  if (!out) dep[u] = 0;
  return out;
}

int run(int s, int t) {
  int ans = 0;
  while (bfs(s, t)) {
    for (int i = 0; i <= n; ++i) cur[i] = head[i];
    ans += dfs(s, t, Inf);
  }
  return ans;
}
void dfs(int u) {
  vis[u] = 1;
  for (int i = head[u]; i; i = e[i].nxt) {
    int v = e[i].v, w = e[i].w;
    if (w && !vis[v]) dfs(v);
  }
}
void init(int n) {
  Dinic::n = n;
  tot = 1;
  for (int i = 0; i <= n; ++i) head[i] = 0;
}
void find(int s, int t) {
  for (int i = 2; i <= tot; i += 2) {
    int v = e[i].v, u = e[i ^ 1].v;
    if (vis[u] == vis[v]) continue;
    if (u == s) pd[v] = 1;
    if (v == t) pd[u] = 1;
  }
}
}

int n, m;
char mp[N][N];
int ban[N][N][2];

inline int id(int x, int y, int p) {
  return (x - 1) * m + y + p * n * m;
}

void solve() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; ++i) scanf("%s", mp[i] + 1);
  for (int i = 1; i <= n * m * 2; ++i) vis[i] = 0;
  for (int i = 1; i <= n * m * 2; ++i) pd[i] = 0;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= m; ++j) ban[i][j][0] = ban[i][j][1] = 0;
  --n, --m;
  if (n == 0 || m == 0) {
    puts("0");
    for (int i = 1; i <= n + 1; ++i) {
      for (int j = 1; j <= m + 1; ++j) {
        if (mp[i][j] == '?') mp[i][j] = 'W';
        printf("%c", mp[i][j]);
      }
      puts("");
    }
    return;
  }
  int ans = 0;
  Dinic::init(n * m * 2 + 1);
  int s = 0, t = n * m * 2 + 1;
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      for (int p : {0, 1}) {
        int q = p ^ 1;
        char P = p ? 'B' : 'W', Q = q ? 'B' : 'W';
        if (mp[i][j] == Q || mp[i + 1][j + 1] == Q
            || mp[i + 1][j] == P || mp[i][j + 1] == P) {
          ban[i][j][p] = 1;
          continue;
        }
        ++ans;
        if (~(i + j + p) & 1) Dinic::add(s, id(i, j, p), 1);
        else Dinic::add(id(i, j, p), t, 1);
        auto check1 = [&](int x, int y) {
          if (ban[x][y][p]) return;
          if (~(x + y + p) & 1) Dinic::add(id(x, y, p), id(i, j, p), Inf);
          else Dinic::add(id(i, j, p), id(x, y, p), Inf);
        };
        auto check2 = [&](int x, int y) {
          if (ban[x][y][q]) return;
          if (~(x + y + q) & 1) Dinic::add(id(x, y, q), id(i, j, p), Inf);
          else Dinic::add(id(i, j, p), id(x, y, q), Inf);
        };
        if (i > 1) check1(i - 1, j);
        if (j > 1) check1(i, j - 1);
        if (i > 1 && j > 1) check2(i - 1, j - 1);
        if (i > 1 && j + 1 <= m) check2(i - 1, j + 1);
        if (p && !ban[i][j][q]) {
          if (~(i + j + p) & 1) Dinic::add(id(i, j, p), id(i, j, q), Inf);
          else Dinic::add(id(i, j, q), id(i, j, p), Inf);
        }
      }
    }
  }
  printf("%d\n", ans - Dinic::run(s, t));
  Dinic::dfs(s);
  Dinic::find(s, t);
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      int fl = -1;
      for (int p : {0, 1}) {
        if (ban[i][j][p] || pd[id(i, j, p)]) continue;
        fl = p;
      }
      if (fl == -1) continue;
      char p = fl ? 'B' : 'W', q = fl ? 'W' : 'B';
      for (int x = 0; x <= 1; ++x)
        for (int y = 0; y <= 1; ++y)
          mp[i + x][j + y] = (x + y) & 1 ? q : p;
    }
  }
  for (int i = 1; i <= n + 1; ++i) {
    for (int j = 1; j <= m + 1; ++j) {
      if (mp[i][j] == '?') mp[i][j] = 'W';
      printf("%c", mp[i][j]);
    }
    puts("");
  }
}
int main() {
  // freopen("matrix.in", "r", stdin);
  // freopen("matrix.out", "w", stdout);
  int t;
  scanf("%d", &t);
  while (t--) {
    solve();
  }
  return 0;
}