add base test functiuon

src/main.rs

@@ -1,6 +1,17 @@
 #![allow()]
 #![no_std]
 #![no_main]
+#![feature(custom_test_frameworks)]
+#![test_runner(crate::test_runner)]
+#![reexport_test_harness_main = "test_main"]
+
+#[cfg(test)]
+pub fn test_runner(tests: &[&dyn Fn()]) {
+    println!("Running {} tests", tests.len());
+    for test in tests {
+        test();
+    }
+}
 mod vga_buffer;
 
 use core::panic::PanicInfo;
@@ -14,7 +25,15 @@ fn panic(info: &PanicInfo) -> ! {
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
     println!("Hello World!");
-    panic!("Nothing to do.");
+    #[cfg(test)]
+    test_main();
 
     loop {}
 }
+
+#[test_case]
+fn trivial_assertion() {
+    print!("trivial assertion... ");
+    assert_eq!(1, 1);
+    println!("[ok]");
+}