Add tests for the VGA buffer

src/main.rs

@@ -58,10 +58,3 @@ pub unsafe fn exit_qemu(exit_code: QemuExitCode) {
     let mut port = Port::new(0xf4);
     port.write(exit_code as u32);
 }
-
-#[test_case]
-fn trivial_assertion() {
-    serial_print!("trivial assertion... ");
-    assert_eq!(1, 1);
-    serial_println!("[ok]");
-}

src/vga_buffer.rs

@@ -2,6 +2,7 @@ use core::fmt;
 use lazy_static::lazy_static;
 use spin::Mutex;
 use volatile::Volatile;
+use crate::{serial_print, serial_println};
 
 lazy_static! {
     /// A global `Writer` instance that can be used for printing to the VGA text buffer.
@@ -169,3 +170,33 @@ pub fn _print(args: fmt::Arguments) {
     use core::fmt::Write;
     WRITER.lock().write_fmt(args).unwrap();
 }
+
+#[test_case]
+fn test_println_simple() {
+    serial_print!("test_println... ");
+    println!("test_println_simple output");
+    serial_println!("[ok]");
+}
+
+#[test_case]
+fn test_println_many() {
+    serial_print!("test_println_many... ");
+    for _ in 0..200 {
+        println!("test_println_many output");
+    }
+    serial_println!("[ok]");
+}
+
+#[test_case]
+fn test_println_output() {
+    serial_print!("test_println_output... ");
+
+    let s = "Some test string that fits on a single line";
+    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_character), c);
+    }
+
+    serial_println!("[ok]");
+}