Integration tests for `marco-core`. Each `.rs` file is a separate `cargo test`
binary that exercises only the public API re-exported from `lib.rs`.
See [`Documentation/testing.md`](../Documentation/testing.md) for:
- ---
```bash
cargo test --locked
cargo test --test commonmark_spec_it --locked
MARCO_SPEC_STRICT=1 cargo test --test commonmark_spec_it --locked
MARCO_SPEC_VERBOSE=1 cargo test --test commonmark_spec_it --locked
```
Spec fixture JSON files live in [`tools/spec/`](../tools/spec/README.md) and
are loaded by `commonmark_spec_it.rs` via `include_str!`.