#include<bits/stdc++.h>
#define inf 100000000
using namespace std;
int TT,n,m,a[103][103],ppp[50003][2];
string sss;
int q[100003],totq,dep[100003],S,T,ans,fx[8][2]={{-1,0},{-1,1},{0,1},{1,1},{1,0},{1,-1},{0,-1},{-1,-1}};
struct Edge{
	int nxt;
	int st;
	int ed;
	int val;
}E[2000003];
int totE=-1,head[100003],cur[100003];
void addEdge(int st,int ed,int v){
	E[++totE].ed=ed;
	E[totE].st=st;
	E[totE].val=v;
	E[totE].nxt=head[st];
	head[st]=totE;
	return;
}
bool bfs(){
	for(int i=1;i<=T;i++){dep[i]=-1;cur[i]=head[i];}
	q[totq=1]=S;
	dep[S]=1;
	for(int i=1;i<=totq;i++){
		for(int j=head[q[i]];j!=-1;j=E[j].nxt){
			if(E[j].val<=0)continue;
			if(dep[E[j].ed]==-1){
				dep[E[j].ed]=dep[q[i]]+1;
				q[++totq]=E[j].ed;
			}
		}
	}
	return (dep[T]!=-1);
}
int dinic(int now,int flow){
	if(flow==0||now==T)return flow;
	int rem=flow,uu=0;
	for(int i=cur[now];i!=-1;i=E[i].nxt){
		cur[now]=E[i].nxt;
		if(E[i].val<=0||dep[E[i].ed]!=dep[now]+1)continue;
		uu=dinic(E[i].ed,min(E[i].val,rem));
		rem-=uu;
		E[i].val-=uu;
		E[i^1].val+=uu;
	}
	return flow-rem;
}
void adde(int st,int ed,int v){
	addEdge(st,ed,v);
	addEdge(ed,st,0);
	return;
}
int f(int X,int Y,int Z){return (n-1)*(m-1)*Z+(X-1)*(m-1)+Y;}
void modify(int X,int Y,int val){
	a[X][Y]=a[X+1][Y]=a[X][Y+1]=a[X+1][Y+1]=val;
	return;
}
void sol(){
	memset(head,-1,sizeof(head));
	totE=-1;
	ans=0;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>sss;
		for(int j=1;j<=m;j++){
			if(sss[j-1]=='?')a[i][j]=-1;
			if(sss[j-1]=='W')a[i][j]=((i^j)&1);
			if(sss[j-1]=='B')a[i][j]=((i^j^1)&1);
		}
	}
	S=2*(n-1)*(m-1)+1;T=S+1;
	for(int i=1;i<n;i++){
		for(int j=1;j<m;j++){
			ppp[f(i,j,0)][0]=ppp[f(i,j,1)][0]=i;
			ppp[f(i,j,0)][1]=ppp[f(i,j,1)][1]=j;
			int flg0=1,flg1=1;
			if(a[i][j]==0||a[i+1][j]==0||a[i][j+1]==0||a[i+1][j+1]==0)flg1=0;
			if(a[i][j]==1||a[i+1][j]==1||a[i][j+1]==1||a[i+1][j+1]==1)flg0=0;
			adde(f(i,j,0),f(i,j,1),inf);
			if(flg0)adde(S,f(i,j,0),1);
			if(flg1)adde(f(i,j,1),T,1);
			ans+=flg0+flg1;
			for(int u=0;u<8;u++){
				if(i+fx[u][0]<1||i+fx[u][0]>=n||j+fx[u][1]<1||j+fx[u][1]>=m)continue;
				adde(f(i,j,0),f(i+fx[u][0],j+fx[u][1],1),inf);
			}
		}
	}
	while(bfs())ans-=dinic(S,inf);
	cout<<ans<<'\n';
	for(int i=0;i<=totE;i++){
		if(dep[E[i].st]!=-1&&dep[E[i].ed]==-1&&E[i].val<=0)continue;
		if(E[i].ed==S||E[i].st==T)continue;
		if(E[i].ed!=T&&E[i].st!=S)continue;
		if(E[i].st==S){
			modify(ppp[E[i].ed][0],ppp[E[i].ed][1],0);
			continue;
		}
		modify(ppp[E[i].st][0],ppp[E[i].st][1],1);
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(a[i][j]==-1)a[i][j]=1;
			if((i^j^a[i][j])&1)cout<<'B';
			else cout<<'W';
		}
		cout<<'\n';
	}
	return;
}
signed main(){
	ios::sync_with_stdio(false);
	cin>>TT;
	while(TT--)sol();
	return 0;
}