import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.BufferedWriter;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.InputStream;

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

    static class DReshitLabirint {
        int n;
        int m;

        public boolean canReach(int i, int j, char[][] map) {
            if (map[i][j] == '#') return false;
            if (map[i][j] == '0') return false;
            if (map[i][j] == '1') return true;
            if (map[i][j] == 'P') return false;
            if (i == n - 1 && j == m - 1) return true;

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

            map[i][j] = 'P';
            boolean cr = false;
            for (int k = 0; k < 4; k++) {
                int nx = i + dx[k];
                int ny = j + dy[k];

                if (nx >= 0 && nx < n && ny >= 0 && ny < m && map[nx][ny] != '#') {
                    cr = canReach(nx, ny, map);
                    if (cr) break;
                }
            }
            map[i][j] = cr ? '1' : '0';
            return cr;
        }

        public void solve(int testNumber, InputReader in, OutputWriter out) {
            n = in.readInt();
            m = in.readInt();

            char[][] map = new char[n][m];

            int badCnt = 0;
            int goodCnt = 0;
            for (int i = 0; i < n; i++) {
                String s = in.readString();
                for (int j = 0; j < m; j++) {
                    map[i][j] = s.charAt(j);
                    if (map[i][j] == 'G') {
                        goodCnt++;
                    }
                    if (map[i][j] == 'B') {
                        badCnt++;
                    }
                }
            }

            if (goodCnt == 0) {
                out.println("Yes");
                return;
            }

            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (map[i][j] == 'B') {
                        if (i - 1 >= 0) {
                            if (map[i - 1][j] == 'G') {
                                out.println("No");
                                return;
                            } else if (map[i - 1][j] != 'B') {
                                map[i - 1][j] = '#';
                            }
                        }

                        if (i + 1 < n) {
                            if (map[i + 1][j] == 'G') {
                                out.println("No");
                                return;
                            } else if (map[i + 1][j] != 'B') {
                                map[i + 1][j] = '#';
                            }
                        }

                        if (j - 1 >= 0) {
                            if (map[i][j - 1] == 'G') {
                                out.println("No");
                                return;
                            } else if (map[i][j - 1] != 'B') {
                                map[i][j - 1] = '#';
                            }
                        }

                        if (j + 1 < m) {
                            if (map[i][j + 1] == 'G') {
                                out.println("No");
                                return;
                            } else if (map[i][j + 1] != 'B') {
                                map[i][j + 1] = '#';
                            }
                        }
                    }
                }
            }

            if (1 == 0) {
                return;
            }

            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (map[i][j] == 'G') {
                        if (!canReach(i, j, map)) {
                            out.println("No");
                            return;
                        }
                    }
                }
            }
            out.println("Yes");
            return;
        }

    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects) {
            for (int i = 0; i < objects.length; i++) {
                if (i != 0) {
                    writer.print(' ');
                }
                writer.print(objects[i]);
            }
        }

        public void println(Object... objects) {
            print(objects);
            writer.println();
        }

        public void close() {
            writer.close();
        }

    }

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

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

        public static boolean isWhitespace(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        private 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 readInt() {
            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 readString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                if (Character.isValidCodePoint(c)) {
                    res.appendCodePoint(c);
                }
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public String next() {
            return readString();
        }

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

        }

    }
}

