// Provided by test-runner lib: Outcome = Pass | Fail(&'static str) | Error(&'static str) Logger = trait { log(&mut self, s: &str) } TestCase = { name: &'static str, f: fn(&mut dyn Logger) -> Outcome } RegistryN = fixed-size array of Option; register(); run_all()

// App writes: fn my_test(log: &mut dyn Logger) -> Outcome { // use assert_eq/assert_ne/assert_true/assert_false/... assert_eq(some_app_fn(), 42) }

// Harness wires: REG.register(TestCase{name: "my_test", f: my_test}); REG.run_all(&mut logger);

Insights from project -

1. static mut is unsafe, it need unsafe block. since rust rules doesnt allow more than one mutable references of any object at a time.since compiler restriction are not possible in unsafe, it can have possible bugs.
2. StaticCell ensures rust rules and unsafe block is not needed. its initialization is via init method which cannot be called again, you use .get and .get_mut for getting references, you cannot call .get_mut again if the first object is alive in the scope
3. using a declarative macro to easily register a new test case - test_case!
4. kept attributes as private for Registry main object and test case object as well, using apis for construction and get attribute calls.
5. using generics with function assert_eq_with where the function passed inside assert api is bound with FnOnce trait, i.e. it can be called only once in function assert_eq_with after which the closure instance is consumed and gives compiletime error when tried recalling as can be seen in the below image
6. you can use cargo run --example quickstart and create sample main process for running examples using library code.
7. you can use parameter in Enums! when you return an enum value, you can also return a paramter with that enum value like below pub enum Outcome { Pass, Fail(&'static str), Error(&'static str), } fail and error enum values can also show messages.
8. this is how you can ensure that standard library code is not linked to the binary and putting a condition that a particular feature std should not be active #![cfg_attr(not(feature = "std"), no_std)]