Create new post about unit testing

src/main.rs

@@ -1,18 +1,25 @@
 #![feature(lang_items)] // required for defining the panic handler
 #![feature(const_fn)] // allow declaring functions as const
 #![no_std] // don't link the Rust standard library
-#![no_main] // disable all Rust-level entry points
+#![cfg_attr(not(test), no_main)] // disable all Rust-level entry points
+#![cfg_attr(test, allow(dead_code, unused_macros))] // allow unused code in test mode
 
 extern crate spin;
 extern crate volatile;
 #[macro_use]
 extern crate lazy_static;
 
+#[cfg(test)]
+extern crate array_init;
+#[cfg(test)]
+extern crate std;
+
 #[macro_use]
 mod vga_buffer;
 
 /// This function is the entry point, since the linker looks for a function
 /// named `_start_` by default.
+#[cfg(not(test))]
 #[no_mangle] // don't mangle the name of this function
 pub extern "C" fn _start() -> ! {
     println!("Hello World{}", "!");
@@ -21,6 +28,7 @@ pub extern "C" fn _start() -> ! {
 }
 
 /// This function is called on panic.
+#[cfg(not(test))]
 #[lang = "panic_fmt"]
 #[no_mangle]
 pub extern "C" fn rust_begin_panic(