// created:  May/15/2024 08:13:56
#include<cstdio>
#include<cctype>
#include<vector>
#define F(i,l,r) for(int i=(l),i##_end=(r);i<i##_end;++i)
#define I128 //||is_same<T,__int128_t>::value||is_same<T,__uint128_t>::value
using namespace std;
template<typename T>enable_if_t<is_integral<T>::value I128,void> readmain(T &x)
{
	bool neg=false;int c=getchar();
	for(;!isdigit(c);c=getchar())if(c=='-')neg=true;
	for(x=0;isdigit(c);c=getchar())x=(T)(10*x+(c-'0'));
	if(neg)x=-x;
}
template<typename T>T& read(T &x){readmain(x);return x;}
template<typename T,typename ...Tr>void read(T &x,Tr&... r){readmain(x);read(r...);}
constexpr int N=105;
namespace flow
{
	constexpr int N=20005,M=110005,INF=0x3fffffff;
	int n,s,t,m,cap[2*M],q[N],qf,qr,dis[N];
	vector<pair<int,int>> adj[N];
	vector<pair<int,int>>::iterator cur[N];
	void init(int n_,int s_,int t_){n=n_;s=s_;t=t_;F(i,0,n)adj[i].clear();m=0;}
	void addedge2(int u,int v,int w)
	{
		cap[m]=w;adj[u].emplace_back(v,m++);
		cap[m]=0;adj[v].emplace_back(u,m++);
	}
	bool bfs()
	{
		F(i,0,n)dis[i]=-1,cur[i]=adj[i].begin();
		qf=qr=0;
		dis[q[qr++]=s]=0;
		while(qf<qr)
		{
			int u=q[qf++];
			for(const pair<int,int> &vw:adj[u])if(cap[vw.second]&&!~dis[vw.first])
				dis[q[qr++]=vw.first]=dis[u]+1;
		}
		return ~dis[t];
	}
	int dfs(int u,int flow)
	{
		if(u==t)return flow;
		int ans=0;
		for(vector<pair<int,int>>::iterator &i=cur[u];i!=adj[u].end();++i)if(dis[i->first]==dis[u]+1&&cap[i->second])
		{
			int newflow=min(flow,cap[i->second]);
			newflow=dfs(i->first,newflow);
			cap[i->second]-=newflow;cap[i->second^1]+=newflow;
			flow-=newflow;ans+=newflow;
			if(!flow)break;
		}
		return ans;
	}
	int dinic()
	{
		int ans=0;
		while(bfs())ans+=dfs(s,INF);
		return ans;
	}
}
int tt,n,m;
char s[N][N];
void conflict(int x1,int y1,int x2,int y2)
{
	int u=x1*(m-1)+y1,v=x2*(m-1)+y2;
	flow::addedge2(2*u+1,2*v+0,1);
	flow::addedge2(2*v+1,2*u+0,1);
}
int main()
{
	read(tt);
	while(tt--)
	{
		read(n,m);
		F(i,0,n)scanf("%s",s[i]);
		F(i,0,n)F(j,0,m)
		{
			if(s[i][j]=='B')s[i][j]='1';
			if(s[i][j]=='W')s[i][j]='0';
		}
		F(i,0,n)F(j,0,m)s[i][j]^=(s[i][j]!='?')&(i^j);
		flow::init(2*(n-1)*(m-1)+2,2*(n-1)*(m-1),2*(n-1)*(m-1)+1);
		F(i,0,n-1)
		{
			F(j,0,m-1)
			{
				int u=i*(m-1)+j;
				flow::addedge2(flow::s,2*u+0,1+(s[i][j]=='1'||s[i][j+1]=='1'||s[i+1][j]=='1'||s[i+1][j+1]=='1'));
				flow::addedge2(2*u+0,2*u+1,2);
				flow::addedge2(2*u+1,flow::t,1+(s[i][j]=='0'||s[i][j+1]=='0'||s[i+1][j]=='0'||s[i+1][j+1]=='0'));
			}
		}
		F(i,0,n-1)F(j,0,m-2)conflict(i,j,i,j+1);
		F(i,0,n-2)F(j,0,m-1)conflict(i,j,i+1,j);
		F(i,0,n-2)F(j,0,m-2)conflict(i,j,i+1,j+1),conflict(i+1,j,i,j+1);
		printf("%d\n",2*(n-1)*(m-1)-flow::dinic());
		F(i,0,n-1)
		{
			F(j,0,m-1)
			{
				int u=6*(i*(m-1)+j);
				flow::cap[u+0]+=s[i][j]=='1'||s[i][j+1]=='1'||s[i+1][j]=='1'||s[i+1][j+1]=='1';
				flow::cap[u+4]+=s[i][j]=='0'||s[i][j+1]=='0'||s[i+1][j]=='0'||s[i+1][j+1]=='0';
			}
		}
		flow::dinic();
		F(i,0,n-1)F(j,0,m-1)if(!~flow::dis[2*(i*(m-1)+j)])s[i][j]=s[i][j+1]=s[i+1][j]=s[i+1][j+1]='0';
		F(i,0,n)F(j,0,m)
		{
			if(s[i][j]=='?')s[i][j]='1';
			s[i][j]^=(s[i][j]!='?')&(i^j);
			if(s[i][j]=='1')s[i][j]='B';
			if(s[i][j]=='0')s[i][j]='W';
		}
		F(i,0,n)puts(s[i]);
	}
	return 0;
}