import java.util.*;
import java.io.*;
import java.text.*;

public class D1265 {

	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		PrintWriter pw = new PrintWriter(System.out);
		int t = sc.nextInt();
		while (t-- > 0) {
			int n = sc.nextInt();
			int m = sc.nextInt();
			char[][] grid = new char[n][];

			for (int i = 0; i < grid.length; i++) {
				grid[i] = sc.next().toCharArray();
			}
			int[] dx = { 0, 0, 1, -1 };
			int[] dy = { 1, -1, 0, 0 };
			boolean valid = true;
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					if (grid[i][j] == 'B') {
						for (int k = 0; k < 4; k++) {
							int nxtx = i + dx[k];
							int nxty = j + dy[k];
							if (nxtx >= 0 && nxty >= 0 && nxtx < n && nxty < m) {
								if (grid[nxtx][nxty] == 'G')
									valid = false;
								else {
									if (grid[nxtx][nxty] == '.')
										grid[nxtx][nxty] = '#';
								}
							}
						}
					}
				}
			}

			boolean[][] temp = new boolean[n][m];
			Queue<int[]> q = new LinkedList<int[]>();
			if (grid[n - 1][m - 1] == '.') {
				q.add(new int[] { n - 1, m - 1 });
				temp[n - 1][m - 1] = true;
			}

			while (!q.isEmpty()) {
				int[] cur = q.poll();
				for (int i = 0; i < 4; i++) {
					int nxtx = cur[0] + dx[i];
					int nxty = cur[1] + dy[i];
					if (nxtx < n && nxtx >= 0 && nxty < m && nxty >= 0
							&& (grid[nxtx][nxty] == '.' || grid[nxtx][nxty] == 'G') && !temp[nxtx][nxty]) {
						temp[nxtx][nxty] = true;
						q.add(new int[] { nxtx, nxty });
					}
				}
			}

			int g = 0;
			boolean ans = true;

			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					if (grid[i][j] == 'G') {
						g++;
						ans &= temp[i][j];
					}
				}
			}
			if (g == 0) {
				pw.println("Yes");
				continue;
			}

//			pw.println(ans +" "+valid);
			pw.println(ans && valid ? "Yes" : "No");

		}
		pw.close();
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(FileReader r) {
			br = new BufferedReader(r);
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

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

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

		public String nextLine() throws IOException {
			return br.readLine();
		}

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

		public int[] nextIntArr(int n) throws IOException {
			int[] arr = new int[n];
			for (int i = 0; i < arr.length; i++)
				arr[i] = nextInt();
			return arr;
		}

		public boolean ready() throws IOException {
			return br.ready();
		}

	}
}
