 
import com.sun.org.apache.xpath.internal.functions.FuncFalse;
import javafx.util.Pair;

import java.io.*;
import java.util.*;

import static java.lang.Math.*;

public class Contest {
    public static class pair implements Comparable<pair> {
        long l;
        long r;


        public pair(long lef, long ri) {
            l = lef;
            r = ri;
        }

        @Override
        public int compareTo(pair p) {
            if (l == p.l)
                return Long.compare(r, p.r);
            return Long.compare(l, p.l);
        }
    }

    static int n, m;
    static ArrayList<Integer>[] adj;
    static int dist[];
    static int parent[];
    static long inf = (long) 1e18;
    static int INF = (int) 1e9;


    public static boolean isSimilar(char[] Arr, int s, int k) {
        for (int i = s; i < k - 1; i++) {
            if (Arr[i + 1] != Arr[i])
                return false;
        }
        return true;
    }

    public static int ciel(int d, int mod) {
        if (d % mod == 0)
            return d / mod;
        return (d / mod) + 1;
    }


    public static long gcd(long u, long v) {
        if (v == 0)
            return u;
        return gcd(v, u % v);
    }

    static int k, Arr[], lefAcc[], riAcc[];
    static PrintWriter pw;

    static long memo[][];
    static char[][] Matrix;
    static int[] dx = new int[]{-1, 1, 0, 0};

    static int[] dy = new int[]{0, 0, -1, 1};


    static boolean valid(int i, int j) {

        return i != -1 && j != -1 && i != n && j != m;

    }


    static boolean[][] vis = new boolean[n][m];

    static void dfs2(int i, int j) {

        vis[i][j] = true;                    //mark as visited

        for (int k = 0; k < 4; ++k) {

            int x = i + dx[k], y = j + dy[k];

            if (valid(x, y) && Matrix[x][y] != '#' && !vis[x][y])

                dfs2(x, y);

        }

    }

    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        pw = new PrintWriter(System.out);
        int t = sc.nextInt();
        while (t-- > 0) {
            n = sc.nextInt();
            m = sc.nextInt();
            Matrix = new char[n][m];
            vis = new boolean[n][m];
            for (int i = 0; i < n; i++) {
                String str = sc.next();
                for (int j = 0; j < m; j++)
                    Matrix[i][j] = str.charAt(j);
            }
            boolean ans = Matrix[n - 1][m - 1] != 'B';
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    if (Matrix[i][j] == 'B')
                        for (int k = 0; k < 4; ++k) {
                            int x = i + dx[k], y = j + dy[k];
                            if (valid(x, y)) {
                                if (Matrix[x][y] == 'G')
                                    ans = false;
                                else if (Matrix[x][y] != 'B')
                                    Matrix[x][y] = '#';
                            }

                        }
            if(Matrix[n-1][m-1]!='#')
            dfs2(n - 1, m - 1);
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++) {
                    if (Matrix[i][j] == 'G' && !vis[i][j])
                        ans = false;
                }

            pw.println(ans ? "Yes" : "No");
        }
        pw.close();

    }

    static class Scanner {
        StringTokenizer st;
        BufferedReader br;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++)
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec)
                        f *= 10;
                }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public boolean ready() throws IOException, IOException {
            return br.ready();
        }

    }
}