Add a write_byte test

src/vga_buffer.rs

@@ -170,4 +170,26 @@ mod test {
             color_code: ColorCode::new(Color::Green, Color::Brown),
         }
     }
+
+    #[test]
+    fn write_byte() {
+        let mut writer = construct_writer();
+        writer.write_byte(b'X');
+        writer.write_byte(b'Y');
+
+        for (i, row) in writer.buffer.chars.iter().enumerate() {
+            for (j, screen_char) in row.iter().enumerate() {
+                let screen_char = screen_char.read();
+                if i == BUFFER_HEIGHT - 1 && j == 0 {
+                    assert_eq!(screen_char.ascii_character, b'X');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else if i == BUFFER_HEIGHT - 1 && j == 1 {
+                    assert_eq!(screen_char.ascii_character, b'Y');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else {
+                    assert_eq!(screen_char, empty_char());
+                }
+            }
+        }
+    }
 }