import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.StringTokenizer;

public class A {
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		int t = sc.nextInt();
		for (int test = 0;  test < t; test++) {
			int n = sc.nextInt(), m = sc.nextInt();
			char[][] a = new char[n][m];
			final int[] DELTAX = {-1, 1, 0, 0}, DELTAY = {0, 0, -1, 1};
			for (int i = 0; i < n; i++) {
				String s = sc.next();
				for (int j = 0; j < m; j++) {
					a[i][j] = s.charAt(j);
				}
			}
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					if (a[i][j] == 'B') {
						for (int pos = 0; pos < 4; pos++) {
							int newi = i+DELTAX[pos];
							int newj = j+DELTAY[pos];
							if (newi<n&&newi>=0&&newj<m&&newj>=0&&a[newi][newj]=='.') {
//								System.out.println("YES");
								a[newi][newj] = '#';
							}
						}
					}
				}
			}
			boolean[][]	isVisited = new boolean[n+5][m+5];
			Deque<Position> st = new ArrayDeque<>();
			if (a[n-1][m-1] != '#') {
				st.add(new Position(n-1, m-1));
				isVisited[n-1][m-1] = true;
			}
			while (!st.isEmpty()) {
				Position p = st.pop();
				for (int i = 0; i < 4; i++) {
					int newx = p.x+DELTAX[i];
					int newy = p.y+DELTAY[i];
					if (newx<n&&newx>=0&&newy<m&&newy>=0) {
						if (a[newx][newy]!='#'&&!isVisited[newx][newy]) {
							st.add(new Position(newx, newy));
							isVisited[newx][newy] = true;
						}
					}
				}
			}
			boolean ans = true;
			for (int i = 0; i < n; i++){
				for (int j = 0; j < m; j++) {
					if ((a[i][j] == 'G' && !isVisited[i][j]) || 
					(a[i][j] == 'B' && isVisited[i][j])) {
						ans = false;
						break;
					}
				}
			}
			if (ans) {
				System.out.println("Yes");
			} else {
				System.out.println("No");
			}
		}
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String next() {
			while (!st.hasMoreTokens())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}
		
		int nextInt() {
			return Integer.parseInt(next());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
}

class Position {
	public int x, y;
	
	public Position(int x, int y) {
		this.x = x;
		this.y = y;
	}
}
