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1//! This module implements manually tracked test coverage, which useful for
2//! quickly finding a test responsible for testing a particular bit of code.
3//!
4//! See https://matklad.github.io/2018/06/18/a-trick-for-test-maintenance.html
5//! for details, but the TL;DR is that you write your test as
6//!
7//! ```no-run
8//! #[test]
9//! fn test_foo() {
10//! covers!(test_foo);
11//! }
12//! ```
13//!
14//! and in the code under test you write
15//!
16//! ```no-run
17//! fn foo() {
18//! if some_condition() {
19//! tested_by!(test_foo);
20//! }
21//! }
22//! ```
23//!
24//! This module then checks that executing the test indeed covers the specified
25//! function. This is useful if you come back to the `foo` function ten years
26//! later and wonder where the test are: now you can grep for `test_foo`.
27
28#[macro_export]
29macro_rules! tested_by {
30 ($ident:ident) => {
31 #[cfg(test)]
32 {
33 crate::marks::marks::$ident.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
34 }
35 };
36}
37
38#[macro_export]
39macro_rules! covers {
40 ($ident:ident) => {
41 let _checker = crate::marks::marks::MarkChecker::new(&crate::marks::marks::$ident);
42 };
43}
44
45#[cfg(test)]
46pub(crate) mod marks {
47 use std::sync::atomic::{AtomicUsize, Ordering};
48
49 pub(crate) struct MarkChecker {
50 mark: &'static AtomicUsize,
51 value_on_entry: usize,
52 }
53
54 impl MarkChecker {
55 pub(crate) fn new(mark: &'static AtomicUsize) -> MarkChecker {
56 let value_on_entry = mark.load(Ordering::SeqCst);
57 MarkChecker {
58 mark,
59 value_on_entry,
60 }
61 }
62 }
63
64 impl Drop for MarkChecker {
65 fn drop(&mut self) {
66 if std::thread::panicking() {
67 return;
68 }
69 let value_on_exit = self.mark.load(Ordering::SeqCst);
70 assert!(value_on_exit > self.value_on_entry, "mark was not hit")
71 }
72 }
73
74 macro_rules! mark {
75 ($ident:ident) => {
76 #[allow(bad_style)]
77 pub(crate) static $ident: AtomicUsize = AtomicUsize::new(0);
78 };
79 }
80
81 mark!(name_res_works_for_broken_modules);
82}