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//! This module implements manually tracked test coverage, which is useful for
//! quickly finding a test responsible for testing a particular bit of code.
//!
//! See <https://matklad.github.io/2018/06/18/a-trick-for-test-maintenance.html>
//! for details, but the TL;DR is that you write your test as
//!
//! ```
//! #[test]
//! fn test_foo() {
//! mark::check!(test_foo);
//! }
//! ```
//!
//! and in the code under test you write
//!
//! ```
//! # use test_utils::mark;
//! # fn some_condition() -> bool { true }
//! fn foo() {
//! if some_condition() {
//! mark::hit!(test_foo);
//! }
//! }
//! ```
//!
//! This module then checks that executing the test indeed covers the specified
//! function. This is useful if you come back to the `foo` function ten years
//! later and wonder where the test are: now you can grep for `test_foo`.
use std::sync::atomic::{AtomicUsize, Ordering};
#[macro_export]
macro_rules! _hit {
($ident:ident) => {{
#[cfg(test)]
{
extern "C" {
#[no_mangle]
static $ident: std::sync::atomic::AtomicUsize;
}
unsafe {
$ident.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
}
}
}};
}
pub use _hit as hit;
#[macro_export]
macro_rules! _check {
($ident:ident) => {
#[no_mangle]
static $ident: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
let _checker = $crate::mark::MarkChecker::new(&$ident);
};
}
pub use _check as check;
pub struct MarkChecker {
mark: &'static AtomicUsize,
value_on_entry: usize,
}
impl MarkChecker {
pub fn new(mark: &'static AtomicUsize) -> MarkChecker {
let value_on_entry = mark.load(Ordering::Relaxed);
MarkChecker { mark, value_on_entry }
}
}
impl Drop for MarkChecker {
fn drop(&mut self) {
if std::thread::panicking() {
return;
}
let value_on_exit = self.mark.load(Ordering::Relaxed);
assert!(value_on_exit > self.value_on_entry, "mark was not hit")
}
}
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