Merge pull request #7607 from sylvestre/uutest-doc

uutests: add a doc

Author: cakebaker

CONTRIBUTING.md

@@ -36,6 +36,8 @@ parts for getting started:
 - [`src/bin/coreutils.rs`](https://github.com/uutils/coreutils/tree/main/src/bin/coreutils.rs): Code for the multicall
   binary.
 - [`docs`](https://github.com/uutils/coreutils/tree/main/docs/src): the documentation for the website
+- [`tests/uutests/`](https://github.com/uutils/coreutils/tree/main/tests/uutests/):
+  Crate implementing the various functions to test uutils commands.
 
 Each utility is defined as a separate crate. The structure of each of these
 crates is as follows:

tests/tests.rs

@@ -3,7 +3,6 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
-// Then override the macro with your constant
 use std::env;
 
 pub const TESTS_BINARY: &str = env!("CARGO_BIN_EXE_coreutils");
@@ -12,6 +11,7 @@ pub const TESTS_BINARY: &str = env!("CARGO_BIN_EXE_coreutils");
 #[ctor::ctor]
 fn init() {
     unsafe {
+        // Necessary for uutests to be able to find the binary
         std::env::set_var("UUTESTS_BINARY_PATH", TESTS_BINARY);
     }
 }