#include<bits/stdc++.h>
#define ll long long
#define db double
#define ull unsigned long long
#define pb push_back
#define pii pair<int, int>
#define FR first
#define SE second
using namespace std;
inline int read() {
  int x = 0; bool op = false;
  char c = getchar();
  while(!isdigit(c))op |= (c == '-'), c = getchar();
  while(isdigit(c))x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
  return op ? -x : x;
}
const int N = 110;
const int M = 1e6 + 10;
const int INF = 1e9;
int n, m, S, T;
char a[N][N], ans[N][N], rev[200];
int id(int x, int y) {return (x - 1) * m + y;}
int etot;
int head[M], to[M], nxt[M], flow[M];
void addedge(int u, int v, int w) {
  to[++etot] = v; flow[etot] = w;
  nxt[etot] = head[u]; head[u] = etot;
  return ;
}
void add(int u, int v, int w) {addedge(u, v, w); addedge(v, u, 0);}
int lev[N], cur[N];
bool bfs() {
  for(int i = 0; i <= T; i++)lev[i] = 0, cur[i] = head[i];
  lev[S] = 1; queue<int> q; q.push(S);
  while(q.empty() == false) {
    int u = q.front(); q.pop();
    for(int i = head[u]; i; i = nxt[i]) {
      if(flow[i] == 0 || lev[to[i]])continue;
      lev[to[i]] = lev[u] + 1;
      if(to[i] == T)return true;
      q.push(to[i]);
    }
  }
  return false;
}
int dinic(int u, int w) {
  if(u == T)return w;
  int v = w;
  for(int i = cur[u]; i && v; i = nxt[i]) {
    cur[u] = i;
    if(flow[i] == 0 || lev[to[i]] != lev[u] + 1)continue;
    int inc = dinic(to[i], min(v, flow[i]));
    if(!inc)lev[to[i]] = 0;
    flow[i] -= inc; flow[i ^ 1] += inc; v -= inc;
  }
  return w - v;
}
int vis[N];
void dfs(int u) {
  if(vis[u])return ; vis[u] = true;
  for(int i = head[u]; i; i = nxt[i])dfs(to[i]);
  return ;
}
void solve() {
  n = read(); m = read(); 
  rev['W'] = 'B'; rev['B'] = 'W'; rev['?'] = '?';
  for(int i = 1; i <= n; i++)scanf("%s", a[i] + 1);
  if(n == 1 || m == 1) {
    puts("0");
    for(int i = 1; i <= n; i++) {
      for(int j = 1; j <= m; j++) {
        if(a[i][j] != '?')ans[i][j] = a[i][j];
        else ans[i][j] = 'W';
        putchar(ans[i][j]);
      }
      putchar('\n');
    }
    return ;
  }
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++) {
      if((i + j) & 1)a[i][j] = rev[a[i][j]];
    }
  }
  S = 0; T = n * m + 1; etot = 1;
  for(int i = 0; i <= T; i++)head[i] = 0;
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++) {
      if(i < n) {
        int w = (j > 1 && j < m ? 2 : 1);
        add(id(i, j), id(i + 1, j), w);
        add(id(i + 1, j), id(i, j), w);
      }
      if(j < m) {
        int w = (i > 1 && i < n ? 2 : 1);
        add(id(i, j), id(i, j + 1), w);
        add(id(i, j + 1), id(i, j), w);
      }
      if(a[i][j] == 'B')add(S, id(i, j), INF);
      if(a[i][j] == 'W')add(id(i, j), T, INF);
    }
  }
  int cnt = 0, v = 0;
  while(bfs())while(v = dinic(S, INF))cnt += v;
  assert(~cnt & 1); cnt /= 2;
  for(int i = 0; i <= T; i++)vis[i] = false;
  dfs(S);
  printf("%d\n", (n - 1) * (m - 1) - cnt);
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++) {
      if(a[i][j] != '?')ans[i][j] = a[i][j];
      else ans[i][j] = vis[id(i, j)] ? 'B' : 'W';
      putchar(((i + j) & 1) ? rev[ans[i][j]] : ans[i][j]);
    }
    putchar('\n');
  }
  return ;
}
int main() {
  int test = read();
  while(test--)solve();
  return 0;
}