import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.AbstractCollection;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.util.LinkedList;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author xwchen
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskD solver = new TaskD();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskD {
        final int inf = 1 << 30;

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int tt = in.nextInt();
            while (tt-- > 0) {
                int n = in.nextInt();
                int m = in.nextInt();
                char[][] c = new char[n][m];
                for (int i = 0; i < n; ++i) {
                    c[i] = in.next().toCharArray();
                }
                for (int i = 0; i < n; ++i) {
                    for (int j = 0; j < m; ++j) {
                        if (c[i][j] == 'B') {
                            setWall(i - 1, j, n, m, c);
                            setWall(i, j - 1, n, m, c);
                            setWall(i + 1, j, n, m, c);
                            setWall(i, j + 1, n, m, c);
                        }
                    }
                }
                LinkedList<Integer> queue = new LinkedList<>();
                int[][] dis = new int[n][m];
                if (c[n - 1][m - 1] == '.') {
                    dis[n - 1][m - 1] = 0;
                    queue.addLast(n - 1);
                    queue.addLast(m - 1);
                }
                for (int i = 0; i < n; ++i) {
                    Arrays.fill(dis[i], inf);
                }
                while (!queue.isEmpty()) {
                    int x = queue.removeFirst();
                    int y = queue.removeFirst();
                    expand(x - 1, y, n, m, queue, dis, c);
                    expand(x, y - 1, n, m, queue, dis, c);
                    expand(x + 1, y, n, m, queue, dis, c);
                    expand(x, y + 1, n, m, queue, dis, c);
                }
                boolean allGood = true;
                boolean allBadNot = true;
                for (int i = 0; i < n; ++i) {
                    for (int j = 0; j < m; ++j) {
                        if (c[i][j] == 'G' && dis[i][j] == inf) {
                            allGood = false;
                        }
                        if (c[i][j] == 'B' && dis[i][j] < inf) {
                            allBadNot = false;
                        }
                    }
                }
                out.println((allGood && allBadNot) ? "Yes" : "No");
            }
        }

        void expand(int x, int y, int n, int m, LinkedList<Integer> queue, int[][] dis, char[][] c) {
            if (inside(x, y, n, m) && dis[x][y] == inf && c[x][y] != '#') {
                queue.addLast(x);
                queue.addLast(y);
                dis[x][y] = 0;
            }
        }

        boolean inside(int x, int y, int n, int m) {
            return x >= 0 && y >= 0 && x < n && y < m;
        }

        void setWall(int x, int y, int n, int m, char[][] c) {
            if (inside(x, y, n, m) && c[x][y] == '.') {
                c[x][y] = '#';
            }
        }

    }

    static class InputReader {
        private BufferedReader reader;
        private StringTokenizer tokenizer = new StringTokenizer("");

        public InputReader(InputStream inputStream) {
            this.reader = new BufferedReader(
                    new InputStreamReader(inputStream));
        }

        public String next() {
            while (!tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return tokenizer.nextToken();
        }

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

    }
}

