B

#include<bits/stdc++.h>
using namespace std;

int main(){
    int tst;
    cin>>tst;
    while(tst--){
        int n, m;
        cin >> n >> m;
        string s[n];

        for (int i = 0; i < n; i++)        cin >> s[i];

        int f = 0;

        for (char x : {'B', 'W'})
        {
            int row_max = 0, col_max = 0, row_min = 1e9, col_min = 1e9;

            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                {
                    if (s[i][j] == x)
                    {
                        row_max = max(row_max, i);
                        row_min = min(row_min, i);
                        col_max = max(col_max, j);
                        col_min = min(col_min, j);
                    }
                }
            }

            if (col_min == 0 && col_max == m-1 && row_min == 0 && row_max == n-1)
            {
                cout << "YES" << endl;
                f = 1;
                break;
            }
        }

        if(!f)
            cout << "NO" << endl;
    }
}