import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author KharYusuf
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastReader in = new FastReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        DSolveTheMaze solver = new DSolveTheMaze();
        int testCount = Integer.parseInt(in.next());
        for (int i = 1; i <= testCount; i++)
            solver.solve(i, in, out);
        out.close();
    }

    static class DSolveTheMaze {
        int[] dx;
        int[] dy;
        boolean[][] vis;
        int n;
        int m;
        char[][] c;

        public void solve(int testNumber, FastReader s, PrintWriter w) {
            n = s.nextInt();
            m = s.nextInt();
            dx = new int[]{1, -1, 0, 0};
            dy = new int[]{0, 0, 1, -1};
            c = new char[n][];
            boolean good = false;
            for (int i = 0; i < n; i++) {
                c[i] = s.next().toCharArray();
                for (char cc : c[i])
                    if (cc == 'G') {
                        good = true;
                        break;
                    }
            }
            vis = new boolean[n][m];
            dfs(n - 1, m - 1);
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (c[i][j] == 'G' && !vis[i][j]) {
                        w.println("No");
                        return;
                    }
                    if (c[i][j] == 'B' && vis[i][j]) {
                        for (int k = 0; k < 4; k++) {
                            int xx = dx[k] + i, yy = dy[k] + j;
                            if (xx >= 0 && xx < n && yy >= 0 && yy < m && c[xx][yy] == '.' && vis[xx][yy]) {
                                c[xx][yy] = '#';
                            }
                        }
                    }
                }
            }
            vis = new boolean[n][m];
            if (c[n - 1][m - 1] != '#') dfs(n - 1, m - 1);
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (c[i][j] == 'G' && !vis[i][j]) {
                        w.println("No");
                        return;
                    }
                    if (c[i][j] == 'B' && vis[i][j]) {
                        w.println("No");
                        return;
                    }
                }
            }
            w.println("Yes");
        }

        void dfs(int x, int y) {
            vis[x][y] = true;
            for (int i = 0; i < 4; i++) {
                int xx = dx[i] + x, yy = dy[i] + y;
                if (xx >= 0 && xx < n && yy >= 0 && yy < m && c[xx][yy] != '#' && !vis[xx][yy]) dfs(xx, yy);
            }
        }

    }

    static class FastReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private FastReader.SpaceCharFilter filter;

        public FastReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {

            if (numChars == -1)
                throw new InputMismatchException();

            if (curChar >= numChars) {

                curChar = 0;

                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }

                if (numChars <= 0)
                    return -1;
            }

            return buf[curChar++];
        }

        public int nextInt() {

            int c = read();

            while (isSpaceChar(c))
                c = read();

            int sgn = 1;

            if (c == '-') {
                sgn = -1;
                c = read();
            }

            int res = 0;

            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();

                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));

            return res * sgn;
        }

        public String next() {

            int c = read();

            while (isSpaceChar(c))
                c = read();

            StringBuilder res = new StringBuilder();

            do {
                res.appendCodePoint(c);
                c = read();
            }
            while (!isSpaceChar(c));

            return res.toString();
        }

        public boolean isSpaceChar(int c) {

            if (filter != null)
                return filter.isSpaceChar(c);

            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }

    }
}

