Split test and source code

[GiggleLiu]

Let tests/ and src/ to have the same file structure and names. Follow the Julia convention to make it cleaner.

[isPANN]

Maybe in Rust, this is not a good design, at least not by literally mirroring src/ under tests/ as many separate integration test files. I asked AI for the best practice.

In Cargo, every tests/*.rs file becomes its own test crate + binary. If you mirror src/ one-to-one, you’ll end up with lots of integration test binaries, which:

• re-link your library repeatedly (slower compile),
• run as separate binaries (longer overall runtime path),
• and still can’t access private / pub(crate) internals.

In Rust,

• Unit tests live under src/ (compiled as part of the crate with cfg(test)), so they can access non-public APIs (private items, pub(crate), etc.). They’re best for white-box testing: validating internal invariants, edge cases, and tricky logic.
• Integration tests live under tests/ and are compiled as separate external crates, so they should focus on user-visible behavior and only use the public API. For larger projects, it’s usually best to keep a single integration test crate/binary (e.g., tests/it/main.rs) and split it into modules, rather than having many separate tests/*.rs files.

Let me propose a better way to make the whole repo cleaner.