Tests: document TestEnv

Author: Firestar99

crates/cargo-gpu/src/test.rs

@@ -8,6 +8,11 @@ use std::io::Write as _;
 use std::path::PathBuf;
 use tempfile::TempDir;
 
+/// `TestEnv` sets up a temp dir in `./target/cargo-gpu-test/` that is used as the cache dir. Not initializing a
+/// `TestEnv` and asking for the cache dir will panic, to ensure you set it up. Calling [`Self::setup_shader_crate`]
+/// or [`Self::setup_shader_crate_with_cargo_toml`] will copy the `shader_crate_template` into the temp dir and return
+/// you the path to it, so each test now has it's unique copy and won't race to change the template in the repo.
+/// Dropping `TestEnv` will clean up the dir, except when panic unwinding, so you can debug failures.
 #[must_use]
 pub struct TestEnv(TempDir);