#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#define ll long long
using namespace std;
const int MN=105;
ll n,m,mp[MN][MN],mpp[MN][MN];
bool op[MN],flag;
char ch;
void write(ll n){if(n<0){putchar('-');write(-n);return;}if(n>9)write(n/10);putchar(n%10+'0');}
ll read(){ll 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 x*f;}
char gc(){char ch=getchar();while(ch!='W'&&ch!='B')ch=getchar();return ch;}
void change(ll x, ll y){
    mpp[x][y]^=1;
    for(int i=1; i<=n; i++) mpp[i][y]^=1;
    for(int i=1; i<=m; i++) mpp[x][i]^=1;
}
void work(){
    for(int i=1; i<=n; i++) for(int j=1; j<=m; j++) mpp[i][j]=mp[i][j];
    for(int i=1; i<=n*m; i++){
        ll x=(i+m-1)/m,y=(i%m==0?m:i%m);
        if(op[i]) change(x,y);
    }
    bool ok=true;
    for(int i=1; i<=n; i++){
        for(int j=1; j<=m; j++) if(!mpp[i][j]){
            ok=false;
            break;
        }
        if(!ok) break;
    }
    if(ok) flag=true; 
}
void dfs(ll step){
    if(step==n*m+1){
        work();
        return;
    }
    op[step]=0;dfs(step+1);if(flag) return;
    op[step]=1;dfs(step+1);if(flag) return;
}
void solve(){
    n=read();m=read();flag=false;
    for(int i=1; i<=n; i++) for(int j=1; j<=m; j++){ch=gc();mp[i][j]=ch=='W'?1:0;}
    dfs(1);
    if(flag) printf("Yes\n");
    else printf("No\n");
}
int main(){
    ll T=read();while(T--)solve();
	return 0;
}