#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<cassert>
#include<set>
#include<random>
#include<chrono>
#include<bitset>
#include<map>
#include<queue>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<string>
#define eb emplace_back

using namespace std;
const int maxn=2e5+10, maxm=1e6+10, inf=2e9+10, P=998244353;
const double eps=1e-10;
typedef long long LL;
typedef unsigned long long ULL;
const LL INF=4e18;
typedef pair<LL, int> pli;
typedef pair<int, int> pii;
typedef pair<LL, LL> pll;
inline int read() {
	int x=0, f=1; char c=getchar();
	for(; c<'0'||c>'9'; c=getchar()) if(c=='-') f=0;
	for(; c>='0'&&c<='9'; c=getchar()) x=x*10+c-'0';
	return f?x:-x;
}
mt19937 rnd((unsigned)chrono::steady_clock::now().time_since_epoch().count());
inline int ksm(int x, int y) {
	int s=1;
	for(; y; y>>=1, x=1LL*x*x%P)
		if(y&1) s=1LL*s*x%P;
	return s;
}
inline int add(int x, int y) {x+=y; return x>=P?x-P:x;}
inline int del(int x, int y) {x-=y; return x<0?x+P:x;}
LL gcd(LL x, LL y) {return y?gcd(y, x%y):x;}


char s[120][120];
const int N=40020, M=130020;
struct pj{int y, nxt, c;} g[M<<1];
int len=1, la[N];
inline void add_e(int x, int y, int c) {
    g[++len].y=y; g[len].nxt=la[x]; la[x]=len; g[len].c=c; swap(x, y);
    g[++len].y=y; g[len].nxt=la[x]; la[x]=len; g[len].c=0;
}
int S, T, h[N], q[N], now[N];
inline int bfs() {
    for(int i=1; i<=T; ++i) now[i]=la[i], h[i]=-1;
    int hd=1, tl=1; q[1]=S; h[S]=1;
    while(hd<=tl) {
        int x=q[hd++];
        for(int i=la[x]; i; i=g[i].nxt) {
            int y=g[i].y;
            if(g[i].c>0&&h[y]==-1) {
                h[y]=h[x]+1;
                if(y==T) return 1;
                q[++tl]=y;
            }
        }
    }
    return 0;
}
int dinic(int x, int f) {
    if(x==T) return f;
    int s=0;
    for(int i=now[x]; i; i=g[i].nxt) {
        int y=g[i].y; now[x]=i;
        if(g[i].c>0&&h[y]==h[x]+1) {
            int tmp=dinic(y, min(g[i].c, f-s));
            g[i].c-=tmp; g[i^1].c+=tmp; s+=tmp;
            if(f==s) return s;
        }
    }
    if(s==0) h[x]=-1;
    return s;
}
int v[N];
void dfs(int x) {
    v[x]=1;
    for(int i=la[x]; i; i=g[i].nxt) {
        int y=g[i].y;
        if(g[i].c>0&&v[y]==0) dfs(y);
    }
}

inline int chk(int x, int y) {
    if(s[x][y]!='?'&&s[x][y+1]!='?'&&s[x][y]==s[x][y+1]) return 1;
    if(s[x][y]!='?'&&s[x+1][y]!='?'&&s[x][y]==s[x+1][y]) return 1;
    if(s[x+1][y+1]!='?'&&s[x][y+1]!='?'&&s[x+1][y+1]==s[x][y+1]) return 1;
    if(s[x+1][y+1]!='?'&&s[x+1][y]!='?'&&s[x+1][y+1]==s[x+1][y]) return 1;
    return 0;
}
inline void sol() {
    int n=read(), m=read();
    for(int i=1; i<=n; ++i) scanf("%s", s[i]+1);

    S=n*m+(n-1)*(m-1)*2+1, T=S+1;

    int ans=0;
    for(int i=1; i<=n; ++i) {
        for(int j=1; j<=m; ++j) {
            int id=(i-1)*m+j;
            if(s[i][j]!='?') {
                if((s[i][j]=='W')^((i+j)&1)) {
                    add_e(id, T, inf);
                } else {
                    add_e(S, id, inf);
                }
            }
        } 
        if(i<n) {
            for(int j=1; j<m; ++j) {
                int id=n*m+(i-1)*(m-1)+j; 
                int t=0; if((i+j)&1) t=1;
                //u0
                int t2=s[i][j]!='W'&&s[i+1][j+1]!='W'&&s[i+1][j]!='B'&&s[i][j+1]!='B';
                int t1=s[i][j]!='B'&&s[i+1][j+1]!='B'&&s[i+1][j]!='W'&&s[i][j+1]!='W';

                if(((i+j)&1)&&t1||((i+j)&1^1)&&t2) {
                    add_e(id, (i-1)*m+j, inf); 
                    add_e(id, (i-1)*m+j+1, inf); 
                    add_e(id, i*m+j, inf); 
                    add_e(id, i*m+j+1, inf);
                    add_e(S, id, 1); ++ans;
                }
                //u1
                t^=1;
                if(((i+j)&1)&&t2||((i+j)&1^1)&&t1) {
                    add_e((i-1)*m+j, id+(n-1)*(m-1), inf); 
                    add_e((i-1)*m+j+1, id+(n-1)*(m-1), inf); 
                    add_e(i*m+j, id+(n-1)*(m-1), inf); 
                    add_e(i*m+j+1, id+(n-1)*(m-1), inf);
                    add_e(id+(n-1)*(m-1), T, 1); ++ans;
                }
            }
        }
    }
    while(bfs()) ans-=dinic(S, inf);
    printf("%d\n", ans);
    for(int i=1; i<=T; ++i) v[i]=0;
    dfs(S);
    for(int i=1; i<=n; ++i, puts(""))
        for(int j=1; j<=m; ++j) {
            if(((i+j)&1)^(v[(i-1)*m+j])) printf("B");
                else printf("W");
        }

    len=1;
    for(int i=1; i<=T; ++i) la[i]=0;
}

int main() {
    int T=read();
    while(T--) sol();
	return 0;
}