Testing Embedded Systems is more difficult than testing standard applications. There are at least two hardware platforms involved: the one that runs the compiler, and the target system. Testing on the development machine is much easier, but it can't test hardware-specific code. Conversely, testing directly on the target system is much harder and requires elaborate hardware setup.

Drone OS supports testing on the development machine out of the box. Drone crates as well as all projects generated with drone new have a special feature, named std. When you run the test recipe:

$ just test

Your program is compiled for your development machine target (usually x86_64-unknown-linux-gnu), and not for your device target (e.g. thumbv7m-none-eabi). And the program is compiled with the std feature enabled. This allows to run standard Rust's test runner.

This way you can use all standard Rust testing options: inline #[test] functions, separate test files under tests/ directory, documentation tests (including compile_fail tests.) Also your tests have access to the std crate.

Though, you should keep in mind that the pointer size in your tests and in the release code will usually differ. This kind of tests is suitable for testing algorithms and business logic. Hardware-specific code often will not even compile. For this, you should use condition compilation like in this snippet from drone-cortexm:

fn main() {
fn wait_for_int() {
    #[cfg(feature = "std")]
    return unimplemented!();
    unsafe { asm!("wfi" :::: "volatile") };