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 r = 0; r < rows; r++) {
                maze[r] = in.next().toCharArray();
            }

            int goodExpected = 0;

            for (int r = 0; r < rows; r++) {
                for (int c = 0; c < cols; c++) {
                    if (maze[r][c] == 'B') {
                        for (int d = 0; d < 4; d++) {
                            int dr = r + dy[d];
                            int dc = c + dx[d];
                            if (inBounds(dr, dc, rows, cols) &&
                                maze[dr][dc] == '.') {
                                maze[dr][dc] = '#';
                            }
                        }
                    } else if (maze[r][c] == 'G') {
                        goodExpected++;
                    }
                }
            }

            // for (int r = 0; r < rows; r++) {
            //     out.println(maze[r]);
            // }
            // out.println();


            int badFound = 0;
            int goodFound = 0;
            LinkedList<Point> bfs = new LinkedList<>();
            boolean seen[][] = new boolean[rows][cols];

            if (maze[rows-1][cols-1] != '#') {
                bfs.add(new Point(rows-1, cols-1));
                seen[rows-1][cols-1] = true;
            }

            while (0 < bfs.size()) {
                Point p = bfs.pollFirst();

                if (maze[p.row][p.col] == 'G') {
                    goodFound++;
                } else if (maze[p.row][p.col] == 'B') {
                    badFound++;
                }

                if (maze[p.row][p.col] != '#') {
                    for (int d = 0; d < 4; d++) {
                        int dr = p.row + dy[d];
                        int dc = p.col + dx[d];
                        if (inBounds(dr, dc, rows, cols) &&
                            ! seen[dr][dc] &&
                            maze[dr][dc] != '#') {

                            bfs.add(new Point(dr, dc));
                            seen[dr][dc] = true;
                        }
                    }
                }
            }

            if (goodExpected == goodFound &&
                badFound == 0) {
                out.println("Yes");
            } else {
                out.println("No");
            }

        }
    }

    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();
    }
}
