/*
	Luogu name: Symbolize
	Luogu uid: 672793
*/
#include<bits/stdc++.h>
//#define int long long
#define pii pair<int,int>
#define x first
#define y second
#define rep1(i,l,r) for(register int i=l;i<=r;++i)
#define rep2(i,l,r) for(register int i=l;i>=r;--i)
#define rep3(i,x,y,z) for(register int i=x[y];~i;i=z[i])
#define rep4(i,x) for(auto i:x)
#define debug() puts("----------")
const int N=3e5+10;
const int M=2e4+10;
const int K=1e2+10;
const int inf=0x3f3f3f3f;
using namespace std;
int T,n,m,k,s,t,h[M],e[N<<1],ne[N<<1],w[N<<1],idx,now[N],dep[N],mp[K][K],st[K][K];
bool vis[M];
int dx[]={-1,-1,-1,0,0,0,1,1,1};
int dy[]={-1,0,1,-1,0,1,-1,0,1};
vector<pii> v0,v1;
int read()
{
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9')
	{
		if(ch=='-') f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
		x=(x<<1)+(x<<3)+(ch^48);
		ch=getchar();
	}
	return f*x;
}
void add(int x,int y,int z)
{
	e[idx]=y;
	ne[idx]=h[x];
	w[idx]=z;
	h[x]=idx++;
	return;
}
void Add(int x,int y,int z)
{
	add(x,y,z);
	add(y,x,0);
	return;
}
bool bfs()
{
	memset(dep,-1,sizeof dep);
	queue<int> q;
	q.push(s);
	dep[s]=0;
	now[s]=h[s];
	while(!q.empty())
	{
		int x=q.front();
		q.pop();
		rep3(i,h,x,ne)
		{
			int to=e[i];
			if(w[i]&&dep[to]==-1)
			{
				dep[to]=dep[x]+1;
				now[to]=h[to];
				q.push(to);
				if(to==t) return 1;
			}
		}
	}
	return 0;
}
int dfs(int x,int sum)
{
	if(x==t) return sum;
	int ans=0;
	rep3(i,now,x,ne)
	{
		int to=e[i];
		now[x]=i;
		if(w[i]&&dep[to]==dep[x]+1)
		{
			int flow=dfs(to,min(sum,w[i]));
			if(!flow) dep[to]=-1;
			w[i]-=flow;
			w[i^1]+=flow;
			ans+=flow;
			sum-=flow;
		}
		if(!sum) break;
	}
	return ans;
}
int Dinic()
{
	int ans=0;
	while(bfs()) ans+=dfs(s,inf);
	return ans;
}
void dfs(int x)
{
	vis[x]=1;
	rep3(i,h,x,ne)
	{
		int to=e[i];
		if(vis[to]||!w[i]) continue;
		dfs(to);
	}
	return;
}
void getans()
{
	idx=0;
	v0.clear();
	v1.clear();
	n=read();
	m=read();
	rep1(i,1,n)
	{
		rep1(j,1,m)
		{
			st[i][j]=0;
			char ch;
			cin>>ch;
			if(ch=='W') mp[i][j]=0;
			if(ch=='B') mp[i][j]=1;
			if(ch=='?') mp[i][j]=2;
			if((i&1)^(j&1)&&ch!='?') mp[i][j]^=1;
		}
	}
	rep1(i,1,n-1)
	{
		rep1(j,1,m-1)
		{
			if(!(mp[i][j]==1||mp[i+1][j]==1||mp[i][j+1]==1||mp[i+1][j+1]==1)) v0.push_back(make_pair(i,j));
			if(!(mp[i][j]==0||mp[i+1][j]==0||mp[i][j+1]==0||mp[i+1][j+1]==0)) 
			{
				st[i][j]=v1.size()+1;
				v1.push_back(make_pair(i,j));
			}
		}
	}
	int l0=v0.size(),l1=v1.size();
	rep1(i,1,l0+l1+2) h[i]=-1,vis[i]=0;
	s=l0+l1+1;
	t=s+1;
	rep1(i,0,l0-1) Add(s,i+1,1);
	rep1(i,0,l1-1) Add(l0+i+1,t,1);
	rep1(i,0,l0-1)
	{
		pii x=v0[i];
		rep1(k,0,8)
		{
			pii t=make_pair(x.x+dx[k],x.y+dy[k]);
			if(t.x<1||t.x>n||t.y<1||t.y>m) continue;
			if(st[t.x][t.y])
			{
//				cout<<i+1<<' '<<l0+st[t.x][t.y]<<"\n";
				Add(i+1,l0+st[t.x][t.y],1);
			}
		}
	}
	printf("%d\n",l0+l1-Dinic());
	dfs(s);
	rep1(i,1,l0+l1)
	{
		if(i<=l0&&vis[i]) 
		{
			pii now=v0[i-1];
			mp[now.x][now.y]=0;
			mp[now.x+1][now.y]=0;
			mp[now.x][now.y+1]=0;
			mp[now.x+1][now.y+1]=0;
		}
		if(i>=l0+1&&!vis[i])
		{
			pii now=v1[i-l0-1];
			mp[now.x][now.y]=1;
			mp[now.x+1][now.y]=1;
			mp[now.x][now.y+1]=1;
			mp[now.x+1][now.y+1]=1;
		}
	}
	rep1(i,1,n)
	{
		rep1(j,1,m)
		{
			if(mp[i][j]==2) mp[i][j]=0;
			if((i&1)^(j&1)) mp[i][j]^=1;
			if(mp[i][j]==0) putchar('W');
			else putchar('B');
		}
		putchar('\n');
	}
	return;
}
signed main()
{
//	freopen("1.in","r",stdin);
//	freopen("1.out","w",stdout);
	T=read();
	while(T--) getans(); 
	return 0;
}