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.util.Collection;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Objects;
import java.util.List;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.Queue;
import java.util.LinkedList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author out_of_the_box
 */
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);
        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[] rd = new int[]{0, -1, 0, 1};
        int[] cd = new int[]{-1, 0, 1, 0};

        public void solve(int testNumber, InputReader in, OutputWriter out) {
            int n = in.nextInt();
            int m = in.nextInt();
            String[] map = new String[n];
            for (int i = 0; i < n; i++) {
                map[i] = in.nextString();
            }
            boolean[][] init = getReachables(n, m, map);
            List<Pair<Integer, Integer>> bads = new ArrayList<>();
            boolean noGood = true;
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (map[i].charAt(j) == 'G') {
                        noGood = false;
                        if (!init[i][j]) {
                            out.println("No");
                            return;
                        }
                    } else if (map[i].charAt(j) == 'B' && init[i][j]) {
                        bads.add(Pair.of(i, j));
                    }
                }
            }
            if (noGood || bads.isEmpty()) {
                out.println("Yes");
                return;
            }
            StringBuilder[] newMap = new StringBuilder[n];
            for (int i = 0; i < n; i++) {
                newMap[i] = new StringBuilder(map[i]);
            }
            for (Pair<Integer, Integer> bad : bads) {
                int bi = bad.getLeft();
                int bj = bad.getRight();
                for (int i = 0; i < 4; i++) {
                    int nr = bi + rd[i];
                    int nc = bj + cd[i];
                    if (nr >= 0 && nr < n && nc >= 0 && nc < m && init[nr][nc]) {
                        if (map[nr].charAt(nc) == 'G') {
                            out.println("No");
                            return;
                        }
                        if (map[nr].charAt(nc) == '.') {
                            newMap[nr].setCharAt(nc, '#');
                        }
                    }
                }
            }
            String[] finalMap = new String[n];
            for (int i = 0; i < n; i++) {
                finalMap[i] = newMap[i].toString();
            }
            boolean[][] finals = getReachables(n, m, finalMap);
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (map[i].charAt(j) == 'B' && finals[i][j]) {
                        out.println("No");
                        return;
                    }
                    if (map[i].charAt(j) == 'G' && !finals[i][j]) {
                        out.println("No");
                        return;
                    }
                }
            }
            out.println("Yes");
        }

        private boolean[][] getReachables(int n, int m, String[] map) {
            Queue<Pair<Integer, Integer>> q = new LinkedList<>();
            boolean[][] ret = new boolean[n][m];
            if (map[n - 1].charAt(m - 1) == '.') {
                ret[n - 1][m - 1] = true;
                q.add(Pair.of(n - 1, m - 1));
            }
            while (!q.isEmpty()) {
                Pair<Integer, Integer> u = q.poll();
                for (int i = 0; i < 4; i++) {
                    int nr = u.getLeft() + rd[i];
                    int nc = u.getRight() + cd[i];
                    if (nr >= 0 && nr < n && nc >= 0 && nc < m && !ret[nr][nc] && map[nr].charAt(nc) != '#') {
                        ret[nr][nc] = true;
                        q.add(Pair.of(nr, nc));
                    }
                }
            }
            return ret;
        }

    }

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

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

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

        }

    }

    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 Pair<L, R> {
        private L left;
        private R right;

        private Pair(L left, R right) {
            this.left = left;
            this.right = right;
        }

        public L getLeft() {
            return left;
        }

        public R getRight() {
            return right;
        }

        public static <A, B> Pair<A, B> of(A a, B b) {
            return new Pair<>(a, b);
        }

        public String toString() {
            return "Pair{" +
                    "left=" + left +
                    ", right=" + right +
                    '}';
        }

        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Pair<?, ?> pair = (Pair<?, ?>) o;
            return Objects.equals(left, pair.left) &&
                    Objects.equals(right, pair.right);
        }

        public int hashCode() {
            return Objects.hash(left, right);
        }

    }
}

