#include <bits/stdc++.h>
#define rep(i, l, r) for (int i (l); i <= r; ++ i)
#define rrp(i, l, r) for (int i (r); i >= l; -- i)
#define pii pair <int, int>
#define eb emplace_back
#define ls p << 1
#define rs ls | 1
#define inf 1000000000
using namespace std;
constexpr int N = 100 + 5;
typedef unsigned long long ull;
typedef long long ll;
inline ll rd () {
  ll x = 0, f = 1;
  char ch = getchar ();
  while (! isdigit (ch)) {
    if (ch == '-') f = -1;
    ch = getchar ();
  }
  while (isdigit (ch)) {
    x = (x << 1) + (x << 3) + ch - 48;
    ch = getchar ();
  }
  return x * f;
}
int n, m;
char s[N][N];
int id[N][N][2];
vector <int> e[N * N << 1];
int col[N * N << 1], match[N * N << 1];
int vis[N * N << 1];
int stk[N * N << 1], top;
int chg[N * N << 1];
bool dfs (int u) {
  for (auto v : e[u]) {
    if (vis[v]) continue;
    vis[v] = 1; stk[++ top] = v;
    if (! match[v] || dfs (match[v])) return match[v] = u, 1;
  } return 0;
}
void dfs (int u, int now) {
  if (col[u] != -1) return ;
  col[u] = now;
  for (auto v : e[u]) dfs (v, ! now);
}
queue <int> q;
int p[N];
void solve () {
  n = rd (), m = rd ();
  rep (i, 1, n) scanf ("%s", s[i] + 1);
  rep (i, 1, n) rep (j, 1, m) rep (k, 0, 1) id[i][j][k] = 0;
  int tot = 0, ans = 0;
  rep (i, 1, n - 1) {
    rep (j, 1, m - 1) {
      if (s[i][j] == '?' || s[i][j + 1] == '?' || s[i + 1][j] == '?' || s[i + 1][j + 1] == '?') {
        if (s[i][j] != 'W' && s[i + 1][j] != 'B' && s[i][j + 1] != 'B' && s[i + 1][j + 1] != 'W') id[i][j][0] = ++ tot;
        if (s[i][j] != 'B' && s[i + 1][j] != 'W' && s[i][j + 1] != 'W' && s[i + 1][j + 1] != 'B') id[i][j][1] = ++ tot;
      } else {
        ans += s[i][j] == s[i + 1][j + 1] && s[i][j] != s[i + 1][j] && s[i][j] != s[i][j + 1];
      }
    }
  }
  rep (i, 1, n - 1) {
    rep (j, 1, m - 1) {
      rep (k, 0, 1) {
        if (! id[i][j][k]) continue;
        if (id[i][j][! k]) e[id[i][j][k]].eb (id[i][j][! k]);
        if (id[i][j + 1][k]) e[id[i][j][k]].eb (id[i][j + 1][k]), e[id[i][j + 1][k]].eb (id[i][j][k]);//,cout<<id[i][j][k]<<" "<<id[i][j+1][k]<<endl;
        if (id[i + 1][j][k]) e[id[i][j][k]].eb (id[i + 1][j][k]), e[id[i + 1][j][k]].eb (id[i][j][k]);//,cout<<id[i][j][k]<<" "<<id[i+1][j][k]<<endl;
        if (id[i + 1][j + 1][! k]) e[id[i][j][k]].eb (id[i + 1][j + 1][! k]), e[id[i + 1][j + 1][! k]].eb (id[i][j][k]);//,cout<<id[i][j][k]<<" "<<id[i+1][j+1][!k]<<endl;
        if (id[i + 1][j - 1][! k]) e[id[i][j][k]].eb (id[i + 1][j - 1][! k]), e[id[i + 1][j - 1][! k]].eb (id[i][j][k]);
      
      }
    }
  }
  fill (col + 1, col + tot + 1, -1);
  mt19937 rnd (time (0));
  rep (i, 1, tot) p[i] = i;
  shuffle (p + 1, p + tot + 1);
  rep (i, 1, tot) shuffle (e[i].begin (), e[i].end (), rnd);
  rep (i, 1, tot) {
    if (col[i] == -1) dfs (i, 0);
  }
  rep (i, 1, tot) {
    if (! col[p[i]]) ans -= dfs (p[i]);
    while (top) vis[stk[top --]] = 0;
  }
  rep (i, 1, tot) if (col[i] && match[i]) match[match[i]] = i;
  rep (i, 1, tot) vis[i] = -1; 
  rep (i, 1, tot) {
    if (! match[i]) {
      vis[i] = 1; 
      for (auto v : e[i]) if (vis[v] == -1) vis[v] = 0, q.push (v);
    }
  }
  while (! q.empty ()) {
    int u = q.front ();
    q.pop ();
    int v = match[u];
    if (vis[v] == -1) {
      vis[v] = 1;
      for (auto w : e[v]) {
        if (vis[w] == -1) vis[w] = 0, q.push (w);
      }
    }
  }
  rep (i, 1, tot) if (vis[i] == -1 && vis[match[i]] == -1 && col[i] == 0) vis[i] = 1;
  rep (i, 1, n - 1) {
    rep (j, 1, m - 1) {
      if (vis[id[i][j][0]] == 1) s[i][j] = 'B', s[i + 1][j] = 'W', s[i][j + 1] = 'W', s[i + 1][j + 1] = 'B';
      if (vis[id[i][j][1]] == 1) s[i][j] = 'W', s[i + 1][j] = 'B', s[i][j + 1] = 'B', s[i + 1][j + 1] = 'W';
    }
  }
  printf ("%d\n", ans + tot);
  rep (i, 1, n) {
    rep (j, 1, m) if (s[i][j] != '?') putchar (s[i][j]); else putchar ('B');
    puts ("");
  } 
  rep (i, 1, tot) e[i].clear (), match[i] = 0, vis[i] = 0;
}
int main () {
  // freopen ("1.in", "r", stdin);
  // freopen ("1.out", "w", stdout);
  for (int T (rd ()); T; -- T) solve ();  
}

answer.code: In function ‘void solve()’:
answer.code:79:11: error: no matching function for call to ‘shuffle(int*, int*)’
   79 |   shuffle (p + 1, p + tot + 1);
      |   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/13/algorithm:61,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:51,
                 from answer.code:1:
/usr/include/c++/13/bits/stl_algo.h:3742:5: note: candidate: ‘template<class _RAIter, class _UGenerator> void std::shuffle(_RAIter, _RAIter, _UGenerator&&)’
 3742 |     shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
      |     ^~~~~~~
/usr/include/c++/13/bits/stl_algo.h:3742:5: note:   template argument deduction/substitution failed:
answer.code:79:11: note:   candidate expects 3 arguments, 2 provided
   79 |   shuffle (p + 1, p + tot + 1);
      |   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~
answer.code:50:23: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   50 |   rep (i, 1, n) scanf ("%s", s[i] + 1);
      |                 ~~~~~~^~~~~~~~~~~~~~~~