unit testing for vga

src/vga_buffer.rs

@@ -155,3 +155,28 @@ impl Writer {
     }
 }
 
+#[test_case]
+fn test_println_simple() {
+    println!("test_println_simple output");
+}
+
+#[test_case]
+fn test_println_many() {
+    for _ in 0..200 {
+        println!("test_println_many output");
+    }
+}
+
+#[test_case]
+fn test_println_output() {
+    let s = "loss and gain is the same";
+    println!("{}", s);
+
+    for (i, c) in s.chars().enumerate() {
+        let screen_char = WRITER.lock()
+            .buffer
+            .chars[BUFFER_HEIGHT - 2][i]
+            .read();
+        assert_eq!(char::from(screen_char.ascii_carachter), c);
+    }
+}