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

public class Solve {
    FastScanner in;
    PrintWriter out;

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

    static boolean inBounds(int row, int col, int rows, int cols) {
        return (0 <= row &&
                0 <= col &&
                row < rows &&
                col < cols);
    }

    static class Point {
        int row, col;
        Point(int r, int c) {
            row = r;
            col = c;
        }
    }

    void solve() {
        int T = in.nextInt();
        while (0 < T--) {
            int rows = in.nextInt();
            int cols = in.nextInt();
            char[][] maze = new char[rows][cols];
            for (int row = 0; row < rows; row++) {
                maze[row] = in.next().toCharArray();
            }

            int totalGood = 0;
            for (int row = 0; row < rows; row++) {
                for (int col = 0; col < cols; col++) {
                    if (maze[row][col] == 'G') {
                        totalGood++;
                    } else if (maze[row][col] == 'B') {
                        for (int d = 0; d < 4; d++) {
                            int drow = row + dy[d];
                            int dcol = col + dx[d];
                            if (inBounds(drow, dcol, rows, cols) &&
                                maze[drow][dcol] == '.') {
                                maze[drow][dcol] = '#';
                            }
                        }
                    }
                }
                // out.println(maze[row]);
            }

            int countBad = 0;
            int countGood = 0;
            LinkedList<Point> bfs = new LinkedList<>();
            boolean[][] seen = new boolean[rows][cols];
            if (maze[rows-1][cols-1] != '#') {
                seen[rows-1][cols-1] = true;
                bfs.add(new Point(rows-1, cols-1));
            }

            while ( ! bfs.isEmpty()) {
                Point curr = bfs.poll();

                if (maze[curr.row][curr.col] == 'G') {
                    countGood++;
                } else if (maze[curr.row][curr.col] == 'B') {
                    countBad++;
                }

                for (int d = 0; d < 4; d++) {
                    int drow = curr.row + dy[d];
                    int dcol = curr.col + dx[d];
                    if (inBounds(drow, dcol, rows, cols) &&
                        ! seen[drow][dcol] &&
                        maze[drow][dcol] != '#') {
                        seen[drow][dcol] = true;
                        bfs.add(new Point(drow, dcol));
                    }
                }
            }

            // out.println(totalGood + " " + countGood + " " + countBad);
            out.println((0 < countBad || countGood != totalGood) ? "No" : "Yes");

        }
    }

    void run() {
        try {
            in = new FastScanner(new File("Solve.in"));
            out = new PrintWriter(new File("Solve.out"));

            solve();

            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    void runIO() {

        in = new FastScanner(System.in);
        out = new PrintWriter(System.out);

        solve();

        out.close();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        public FastScanner(InputStream f) {
            br = new BufferedReader(new InputStreamReader(f));
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return null;
                st = new StringTokenizer(s);
            }
            return st.nextToken();
        }

        boolean hasMoreTokens() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return false;
                st = new StringTokenizer(s);
            }
            return true;
        }

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

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = in.nextInt();
            }
            return a;
        }

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

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = in.nextLong();
            }
            return a;
        }

        BigInteger nextBigInteger() {
            return new BigInteger(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        double[] nextDoubleArray(int n) {
            double[] a = new double[n];
            for (int i = 0; i < n; i++) {
                a[i] = in.nextDouble();
            }
            return a;
        }

    }

    public static void main(String[] args) {
        new Solve().runIO();
    }
}
