refactor: tests on host with less stuff disabled

examples/test-on-host.rs

@@ -1,15 +1,20 @@
+//! This example shows how a embedded program can be written that is testable on the host with
+//! libtest.
+//!
+//! The tests can be run with:
+//! ```bash
+//! cargo test --example=test-on-host --target=x86_64-unknown-linux-gnu
+//! ```
+
 #![cfg_attr(not(test), no_main)]
 #![no_std]
 
 #[cfg(not(test))]
 extern crate panic_halt;
 
-#[cfg(not(test))]
-use cortex_m_rt::entry;
 use hal::{pac, prelude::*, rcc::Config};
 
-#[cfg(not(test))]
-#[entry]
+#[cfg_attr(not(test), cortex_m_rt::entry)] // this is the entrypoint unless testing
 fn main() -> ! {
     let dp = pac::Peripherals::take().unwrap();
     let cp = cortex_m::Peripherals::take().unwrap();
@@ -31,21 +36,24 @@ fn main() -> ! {
         led.set_high().unwrap();
         delay.delay_ms(500_u16);
 
+        let important_number = some_function(19);
+        delay.delay_ms(important_number as u16);
+
         led.set_low().unwrap();
         delay.delay_ms(500_u16);
     }
 }
 
-#[cfg(test)]
-fn main() -> ! {
-    loop {}
+fn some_function(num: i32) -> i32 {
+    num * 2
 }
 
 #[cfg(test)]
 mod tests {
+    use crate::some_function;
 
     #[test]
     fn test_it_works() {
-        assert!(true)
+        assert_eq!(some_function(9), 18)
     }
 }